<SUBMISSION>
<ACCESSION-NUMBER>0001104659-05-014790
<TYPE>8-K
<PUBLIC-DOCUMENT-COUNT>3
<PERIOD>20050401
<ITEMS>8.01
<ITEMS>9.01
<FILING-DATE>20050401
<DATE-OF-FILING-DATE-CHANGE>20050401
<FILER>
<COMPANY-DATA>
<CONFORMED-NAME>AEROGEN INC
<CIK>0001039160
<ASSIGNED-SIC>3841
<IRS-NUMBER>330488580
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>8-K
<ACT>34
<FILE-NUMBER>000-31913
<FILM-NUMBER>05726613
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>2071 STIERLIN COURT
<CITY>MOUNTAIN VIEW
<STATE>CA
<ZIP>94043
<PHONE>650 864-7300
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>2071 STIERLIN COURT
<CITY>MOUNTAIN VIEW
<STATE>CA
<ZIP>94043
</MAIL-ADDRESS>
</FILER>
<DOCUMENT>
<TYPE>8-K
<SEQUENCE>1
<FILENAME>a05-6170_18k.htm
<DESCRIPTION>8-K
<TEXT>
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<p align="center" style="border:none;margin:0in 0in .0001pt;padding:0in;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

</div>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">UNITED
STATES<br>
SECURITIES AND EXCHANGE COMMISSION</font></b></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Washington,
D. C.&nbsp; 20549</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">FORM
8-K</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="3" face="Times New Roman" style="font-size:12.0pt;font-weight:bold;">CURRENT
REPORT</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="3" face="Times New Roman" style="font-size:12.0pt;font-weight:bold;">Pursuant
to Section&nbsp;13 or 15(d) of the<br>
Securities Exchange Act of 1934</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Date of Report
(Date of earliest event reported):&nbsp;<b><font style="font-weight:bold;">April
1, 2005</font></b></font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">AEROGEN,
INC.</font></b></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(Exact name of
registrant as specified in its charter)</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<table border="0" cellspacing="0" cellpadding="0" width="100%" style="border-collapse:collapse;width:100.0%;">
 <tr>
  <td width="100%" colspan="3" valign="top" style="padding:0in 0in 0in 0in;width:100.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Delaware</font></b></p>
  </td>
 </tr>
 <tr>
  <td width="100%" colspan="3" valign="top" style="padding:0in 0in 0in 0in;width:100.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(State or other
  jurisdiction of incorporation)</font></p>
  </td>
 </tr>
 <tr>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="2%" valign="bottom" style="padding:0in 0in 0in 0in;width:2.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
 </tr>
 <tr>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">0-31913</font></b></p>
  </td>
  <td width="2%" valign="bottom" style="padding:0in 0in 0in 0in;width:2.0%;">
  <p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>
  </td>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">33-0488580</font></b></p>
  </td>
 </tr>
 <tr>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(Commission File
  No.)</font></p>
  </td>
  <td width="2%" valign="bottom" style="padding:0in 0in 0in 0in;width:2.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>
  </td>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(IRS Employer
  Identification No.)</font></p>
  </td>
 </tr>
 <tr>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="2%" valign="bottom" style="padding:0in 0in 0in 0in;width:2.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
 </tr>
 <tr>
  <td width="100%" colspan="3" valign="top" style="padding:0in 0in 0in 0in;width:100.0%;">
  <p align="center" style="margin-left:0in;margin-right:0in;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">2071
  Stierlin Court, Suite 100<br>
  Mountain View, CA 94043</font></b></p>
  </td>
 </tr>
 <tr>
  <td width="100%" colspan="3" valign="top" style="padding:0in 0in 0in 0in;width:100.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(Address of
  principal executive offices and zip code)</font></p>
  </td>
 </tr>
 <tr>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="2%" valign="bottom" style="padding:0in 0in 0in 0in;width:2.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="49%" valign="top" style="padding:0in 0in 0in 0in;width:49.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
 </tr>
 <tr>
  <td width="100%" colspan="3" valign="top" style="padding:0in 0in 0in 0in;width:100.0%;">
  <p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Registrant&#146;s
  telephone number, including area code: <b><font style="font-weight:bold;">(650)&nbsp;864-7300</font></b></font></p>
  </td>
 </tr>
</table>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Check the appropriate box
below if the Form 8-K filing is intended to simultaneously satisfy the filing
obligation of the registrant under any of the following provisions (see General
Instruction A.2. below):</font></p>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font> Written communications pursuant to Rule 425
under the Securities Act (17 CFR 230.425)</p>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font> Soliciting material pursuant to Rule 14a-12
under the Exchange Act (17 CFR 240.14a-12)</p>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font> Pre-commencement communications pursuant to
Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))</p>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font> Pre-commencement communications pursuant to
Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))</p>

<div style="border:none;border-bottom:double windowtext 9.0pt;padding:0in 0in 0in 0in;">

<p style="border:none;margin:0in 0in .0001pt;padding:0in;text-autospace:none;"><font size="2" face="Times New Roman">&nbsp;</font></p>

</div>

<p style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<div style="margin:0in 0in .0001pt;text-autospace:none;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">

<hr size="2" width="100%" noshade color="gray" align="left">

</font></div>

</div>
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<div style="font-family:Times New Roman;">

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Item
8.01.</font></b><b><font size="1" style="font-size:3.0pt;font-weight:bold;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font></b><b><font size="2" style="font-size:10.0pt;font-weight:bold;">Other
Events.</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">On
April 1, 2005, Jane Shaw, Chairman of Aerogen, Inc. (the &#147;Company&#148;)&#160; delivered a letter (the &#147;Letter&#148;) to Mitchell
Kaye of Xmark Funds, responding to a letter from Mr. Kaye to the Aerogen Board
of Directors dated March 29, 2005 which had been filed as an exhibit to
Amendment No. 3 to a Form 13D filed by Xmark Funds on March 30, 2005. &nbsp; A
copy of the Letter is attached as Exhibit 99.1 to this current report and is
incorporated herein by reference.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">The
information in Item 8.01 of this Report on Form 8-K, including the exhibit
hereto, shall not be deemed to be &#147;filed&#148; for purposes of Section 18 of the
Securities Exchange Act of 1934, as amended, or otherwise subject to the
liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act
of 1933, as amended. The information contained in this Item 8.01 and in the
accompanying exhibit shall not be incorporated by reference into any filing
with the U.S. Securities and Exchange Commission made by Aerogen, Inc., whether
made before or after the date hereof, regardless of any general incorporation
language in such filing.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Item 9.01.</font></b><b><font size="1" style="font-size:3.0pt;font-weight:bold;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font></b><b><font style="font-weight:bold;">Financial Statements and
Exhibits.</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(c)</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font>Exhibits:</p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt 74.8pt;text-indent:-37.4pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">99.1</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font>Letter,
dated April 1, 2005, from Jane E. Shaw, Chairman of the Board of Directors of
Aerogen, Inc., to Mitchell Kaye of Xmark Funds.</p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">2</font></p>

<div style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">

<hr size="2" width="100%" noshade color="gray" align="left">

</font></div>

</div>
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<div style="font-family:Times New Roman;">

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">SIGNATURE</font></b></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;">&nbsp;</p>

<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Pursuant to the
requirements of the Securities Exchange Act of 1934, the registrant has duly
caused this report to be signed on its behalf by the undersigned, thereunto
duly authorized.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<table border="0" cellspacing="0" cellpadding="0" width="100%" style="border-collapse:collapse;width:100.0%;">
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>
  </td>
  <td width="44%" colspan="5" valign="top" style="padding:0in .7pt 0in .7pt;width:44.0%;">
  <p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">AEROGEN</font></b><font size="2" style="font-size:10.0pt;">, <b><font style="font-weight:bold;">INC.</font></b></font></p>
  </td>
 </tr>
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="44%" colspan="5" valign="top" style="padding:0in .7pt 0in .7pt;width:44.0%;">
  <p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">&nbsp;</font></b></p>
  </td>
 </tr>
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
  <td width="44%" colspan="5" valign="top" style="padding:0in .7pt 0in .7pt;width:44.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
  </td>
 </tr>
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Dated:&nbsp; April 1,
  2005</font></p>
  </td>
  <td width="3%" valign="top" style="padding:0in .7pt 0in .7pt;width:3.32%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">By:</font></p>
  </td>
  <td width="20%" colspan="3" valign="top" style="border:none;border-bottom:solid windowtext 1.0pt;padding:0in .7pt 0in .7pt;width:20.34%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">/s/ Robert S. Breuil</font></p>
  </td>
  <td width="20%" valign="top" style="padding:0in .7pt 0in .7pt;width:20.34%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>
  </td>
 </tr>
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>
  </td>
  <td width="5%" colspan="3" valign="top" style="padding:0in .7pt 0in .7pt;width:5.52%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Name: </font></p>
  </td>
  <td width="38%" colspan="2" valign="top" style="padding:0in .7pt 0in .7pt;width:38.48%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Robert S. Breuil</font></p>
  </td>
 </tr>
 <tr>
  <td width="56%" valign="top" style="padding:0in .7pt 0in .7pt;width:56.0%;">
  <p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>
  </td>
  <td width="4%" colspan="2" valign="top" style="padding:0in .7pt 0in .7pt;width:4.26%;">
  <p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Title:</font></p>
  </td>
  <td width="39%" colspan="3" valign="top" style="padding:0in .7pt 0in .7pt;width:39.74%;">
  <p style="margin-left:0in;margin-right:0in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Chief
  Financial Officer and Vice<br>
  President of Corporate Development</font></p>
  </td>
 </tr>
 <tr height="0">
  <td width="419" style="border:none;"></td>
  <td width="25" style="border:none;"></td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">3</font></p>

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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">EXHIBITS</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt 74.8pt;text-indent:-37.4pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">99.1</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font>Letter,
dated April 1, 2005, from Jane E. Shaw, Chairman of the Board of Directors of
Aerogen, Inc., to Mitchell Kaye of Xmark Funds.</p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">4</font></p>

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<p align="right" style="margin:0in 0in .0001pt;text-align:right;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Exhibit&nbsp;99.1</font></b></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman"><img width="119" height="68" src="g61701mmimage002.gif"></font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">April&nbsp;1,
2005</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><u><font size="2" face="Times New Roman" style="font-size:10.0pt;">Via E-Mail&nbsp;&amp; Facsimile (203) 653-2501</font></u></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Mitchell
Kaye<br>
Chief Investment Officer<br>
XMark Funds<br>
301 Tresser Boulevard, Suite&nbsp;1320<br>
Stamford, CT&#160; 06901</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Dear
Mr.&nbsp;Kaye:</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">On
behalf of the Board of Directors of Aerogen,&nbsp;Inc., I am writing in
response to your letter of March&nbsp;29, 2005.&#160;
The Board was uniformly surprised and disappointed to receive such a
letter from you, written as it was without the benefit of current information
about what actions have been and are being taken by Aerogen and in light of
your private opposition in the past to some of the very actions you are now
recommending.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Since
early December, you have consistently refused to receive any further
information about strategic and value-creating alternatives being pursued by
Aerogen, arguing that you wanted to become free to trade Aerogen stock in the
market after the material non-public information you had earlier requested
entered the public domain.&#160; In addition,
you have repeatedly refused Aerogen&#146;s request that you identify one or more
representatives to join its Board of Directors and constructively participate
in the important decisions about the best way to maximize stockholder value.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">It
is apparent from the late Form&nbsp;13D filings you made this week that you
have been engaging in efforts for some time to sell your shares of Aerogen
stock, without disclosing those transactions to the market as required under
the Securities Exchange Act of 1934.&#160;
Your letter reveals no understanding of Aerogen or its business or the
viable alternatives now confronting the Board, which comes as no surprise since
no representative of Xmark has ever visited Aerogen or met in person with
management to discuss the business, other than one meeting in October&nbsp;2004
with myself and our CFO, Robert Breuil.&#160;
Indeed, early last month you failed to show up for a meeting you had
requested with me in New York City.&#160; We
believe that the only real reason you are upset has nothing to do with the
actions taken or not taken by the Board, but is because our stock price did not
surge immediately following the financing as you expected and enable you to
quickly liquidate your position at values your hedge funds would find
attractive.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">The
Aerogen Board has acted proactively and responsibly since the time of your
investment in 2004 to do what it believed was best for all stockholders, not
just Xmark</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="font-size:10.0pt;margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Aerogen,&nbsp;Inc.</font></b>&#160; 2071 Stierlin Court&#160; Suite&nbsp;100 Mountain View, CA 94043&#160; <b><font style="font-weight:bold;">phone</font></b>
650.864.7300&#160; <b><font style="font-weight:bold;">fax</font></b> 650.864.7350 <b><font style="font-weight:bold;">www</font></b>.aerogen.com</p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<div style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">

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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">and
the holders of the Series&nbsp;A-1 Preferred Stock.&#160; Notwithstanding the threats and
mischaracterizations in your recent letter, the Board intends to continue to
faithfully discharge its duties.&#160; We
would reiterate our invitation to you to join the Aerogen Board and participate
in the discussions and important decisions the Board is facing over the next
several months if you believe you can add constructively to the debate.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;page-break-after:auto;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Sincerely,</font></p>

<p style="margin:0in 0in .0001pt;page-break-after:auto;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<table border="0" cellspacing="0" cellpadding="0" width="100%" style="border-collapse:collapse;width:100.0%;">
 <tr>
  <td width="13%" valign="top" style="border:none;border-bottom:solid windowtext 1.0pt;padding:0in .7pt 0in .7pt;width:13.06%;">
  <p style="margin:0in 0in .0001pt;page-break-after:auto;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">/s/ Jane E. Shaw</font></p>
  </td>
  <td width="86%" valign="top" style="padding:0in .7pt 0in .7pt;width:86.94%;">
  <p style="margin:0in 0in .0001pt;page-break-after:auto;"><font size="1" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>
  </td>
 </tr>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Jane
E. Shaw, Chairman</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Aerogen,&nbsp;Inc.</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">cc:&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Board of Directors</font></p>

<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>

<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">2</font></p>

<div style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">

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