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                                                                     EXHIBIT 2.1

                          AGREEMENT AND PLAN OF MERGER

                  THIS AGREEMENT AND PLAN OF MERGER (hereinafter called the
"Merger Agreement") is made as of _____________, 1996 by and between STERITECH,
INC., a California corporation ("Steritech"), and CERUS CORPORATION, a Delaware
corporation ("Cerus"). Steritech and Cerus are sometimes referred to as the
"Constituent Corporations."

                  The authorized capital stock of Steritech consists of four
million six hundred eighty-one thousand eight hundred thirty-three (4,681,833)
shares of Common Stock and three million one hundred ninety-nine thousand nine
hundred forty-two (3,199,942) shares of Preferred Stock. The authorized capital
stock of Cerus consists of fifty million (50,000,000) shares of Common Stock,
$.001 par value, and five million (5,000,000) shares of Preferred Stock, $.001
par value.

                  The directors of the Constituent Corporations deem it
advisable and to the advantage of said corporations that Steritech merge into
Cerus upon the terms and conditions herein provided.

                  NOW, THEREFORE, the parties do hereby adopt the plan of
reorganization encompassed by this Merger Agreement and do hereby agree that
Steritech shall merge into Cerus on the following terms, conditions and other
provisions:

1.                TERMS AND CONDITIONS.

                  (A) MERGER. Steritech shall be merged with and into Cerus (the
"Merger"), and Cerus shall be the surviving corporation (the "Surviving
Corporation") effective at [_____ a/p.m.] (Eastern Standard Time) on
_________________, 1996 (the "Effective Time").

                  (B) SUCCESSION. At the Effective Time, Cerus shall continue
its corporate existence under the laws of the State of Delaware, and the
separate existence and corporate organization of Steritech, except insofar as it
may be continued by operation of law, shall be terminated and cease.

                  (C) TRANSFER OF ASSETS AND LIABILITIES. At the Effective Time,
the rights, privileges, powers and franchises, both of a public as well as of a
private nature, of each of the Constituent Corporations shall be vested in and
possessed by the Surviving Corporation, subject to all of the disabilities,
duties and restrictions of or upon each of the Constituent Corporations; and all
and singular rights, privileges, powers and franchises of each of the
Constituent Corporations, and all property, real, personal and mixed, of each of
the Constituent Corporations, and all debts due to each of the Constituent
Corporations on whatever account, and all things in action or belonging to each
of the Constituent Corporations shall be transferred to and vested in the
Surviving Corporation; and all property, rights, privileges, powers and
franchises, and all and every other interest, shall be thereafter the property
of the Surviving Corporation as they were of the Constituent Corporations, and
the title to any real estate vested by deed or otherwise in either of the
Constituent Corporations shall not revert or be in any way

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impaired by reason of the Merger; provided, however, that the liabilities of the
Constituent Corporations and of their shareholders, directors and officers shall
not be affected and all rights of creditors and all liens upon any property of
either of the Constituent Corporations shall be preserved unimpaired, and any
claim existing or action or proceeding pending by or against either of the
Constituent Corporations may be prosecuted to judgment as if the Merger had not
taken place except as they may be modified with the consent of such creditors
and all debts, liabilities and duties of or upon each of the Constituent
Corporations shall attach to the Surviving Corporation, and may be enforced
against it to the same extent as if such debts, liabilities and duties had been
incurred or contracted by it.

                  (D) COMMON STOCK OF STERITECH AND CERUS. At the Effective
Time, by virtue of the Merger and without any further action on the part of the
Constituent Corporations or their shareholders, (i) each share of Common Stock
of Steritech issued and outstanding immediately prior thereto shall be changed
and converted into _____ fully paid and nonassessable share[s] of Common Stock
of Cerus; and (ii) each share of Common Stock of Cerus issued and outstanding
immediately prior thereto shall be canceled and returned to the status of
authorized but unissued shares.

                  (E) PREFERRED STOCK OF STERITECH. At the Effective Time, by
virtue of the Merger and without any further action on the part of the
Constituent Corporations or their shareholders, (i) each share of Series A
Preferred Stock of Steritech issued and outstanding immediately prior thereto
shall be changed and converted into one fully paid and nonassessable share of
Series A Preferred Stock of Cerus, (ii) each share of Series B Preferred Stock
of Steritech issued and outstanding immediately prior thereto shall be changed
and converted into one fully paid and nonassessable share of Series B Preferred
Stock of Cerus, (iii) each share of Series C Preferred Stock of Steritech issued
and outstanding immediately prior thereto shall be changed and converted into
one fully paid and nonassessable share of Series C Preferred Stock of Cerus,
(iv) each share of Series D Preferred Stock of Steritech issued and outstanding
immediately prior thereto shall be changed and converted into one fully paid and
nonassessable share of Series D Preferred Stock of Cerus, and (v) each share of
Series E Preferred Stock of Steritech issued and outstanding immediately prior
thereto shall be changed and converted into one fully paid and nonassessable
share of Series E Preferred Stock of Cerus.

                  (F) STOCK CERTIFICATES. At and after the Effective Time, all
of the outstanding certificates which prior to that time represented shares of
the Common Stock and Preferred Stock of Steritech shall be deemed for all
purposes to evidence ownership of and to represent the shares of Cerus into
which the shares of Steritech represented by such certificates have been
converted as herein provided and shall be so registered on the books and records
of the Surviving Corporation or its transfer agents. The registered owner of any
such outstanding stock certificate shall, until such certificate shall have been
surrendered for transfer or conversion or otherwise accounted for to the
Surviving Corporation or its transfer agent, have and be entitled to exercise
any voting and other rights with respect to and to receive any dividend and
other distributions upon the shares of Cerus evidenced by such outstanding
certificate as above provided.

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                  (G) WARRANTS OF STERITECH. At and after the Effective Time,
the outstanding Warrants which prior to that time represented Warrants of
Steritech shall be deemed for all purposes to evidence ownership of and to
represent Warrants of Cerus and shall be so registered on the books and records
of the Surviving Corporation or its transfer agents.

                  (H) OPTIONS OF STERITECH. At the Effective Time, the Surviving
Corporation will assume and continue all of Steritech' stock option plans in
existence at the Effective Time, including but not limited to the 1992 Stock
Option Plan (restated as the 1996 Equity Incentive Plan) and the outstanding
options to purchase Common Stock of Steritech, including without limitation all
options outstanding under such stock option plans and any other outstanding
options, shall become options to purchase shares of Common Stock of Cerus,
subject to applicable adjustment provisions with respect to the number of and
price per share, with no other changes in the terms and conditions of such
options. Effective at the Effective Time, Cerus hereby assumes the outstanding
and unexercised portions of such options and the obligations of Steritech with
respect thereto.

                  (I) EMPLOYEE BENEFIT PLANS. At the Effective Time, the
Surviving Corporation shall assume all obligations of Steritech under any and
all employee benefit plans in effect as of the Effective Time with respect to
which employee rights or accrued benefits are outstanding as of such time,
including, but not limited to the Employee Stock Purchase Plan; provided,
however, that _____ share[s] Common Stock of Cerus shall be substituted for each
share of Common Stock of Steritech (if any) thereunder. At the Effective Time,
the Surviving Corporation shall adopt and continue in effect all such employee
benefit plans upon the same terms and conditions as were in effect immediately
prior to the Merger and shall reserve that number of shares of Cerus Common
Stock with respect to each such employee benefit plan as is equal to the number
of shares of Steritech Common Stock (if any) so reserved at the Effective Time.

2.                CHARTER DOCUMENTS, DIRECTORS AND OFFICERS.

                  (A) CERTIFICATE OF INCORPORATION AND BYLAWS. The Certificate
of Incorporation and Bylaws of Cerus in effect at the Effective Time shall
continue to be the Certificate of Incorporation and Bylaws of the Surviving
Corporation.

                  (B) DIRECTORS. The directors of Steritech immediately
preceding the Effective Time shall become the directors of the Surviving
Corporation at and after the Effective Time to serve until the expiration of
their terms and until their successors are elected and qualified.

                  (C) OFFICERS. The officers of Steritech immediately preceding
the Effective Time shall become the officers of the Surviving Corporation at and
after the Effective Time to serve at the pleasure of its Board of Directors.

3.                MISCELLANEOUS.

                  (A) FURTHER ASSURANCES. From time to time, and when required
by the Surviving Corporation or by its successors and assigns, there shall be
executed and delivered on behalf of

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Steritech such deeds and other instruments, and there shall be taken or caused
to be taken by it such further and other action, as shall be appropriate or
necessary in order to vest or perfect in or to conform of record or otherwise,
in the Surviving Corporation the title to and possession of all the property,
interests, assets, rights, privileges, immunities, powers, franchises and
authority of Steritech and otherwise to carry out the purposes of this Merger
Agreement, and the officers and directors of the Surviving Corporation are fully
authorized in the name and on behalf of Steritech or otherwise to take any and
all such action and to execute and deliver any and all such deeds and other
instruments.

                  (B) AMENDMENT. At any time before or after approval by the
shareholders of Steritech, this Merger Agreement may be amended in any manner
(except that, after the approval of the Merger Agreement by the shareholders of
Steritech, the principal terms may not be amended without the further approval
of the shareholders of Steritech) as may be determined in the judgment of the
respective Board of Directors of Cerus and Steritech to be necessary, desirable,
or expedient in order to clarify the intention of the parties hereto or to
effect or facilitate the purpose and intent of this Merger Agreement.

                  (C) CONDITIONS TO MERGER. The obligation of the Constituent
Corporations to effect the transactions contemplated hereby is subject to
satisfaction of the following conditions (any or all of which may be waived by
either of the Constituent Corporations in its sole discretion to the extent
permitted by law):

                        (I) the Merger shall have been approved by the
shareholders of Steritech in accordance with applicable provisions of the
General Corporation Law of the State of California; and

                        (II) Steritech, as sole stockholder of Cerus, shall have
approved the Merger in accordance with the General Corporation Law of the State
of Delaware; and

                        (III) any and all consents, permits, authorizations,
approvals, and orders deemed in the sole discretion of Steritech to be material
to consummation of the Merger shall have been obtained.

                  (D) ABANDONMENT OR DEFERRAL. At any time before the Effective
Time, this Merger Agreement may be terminated and the Merger may be abandoned by
the Board of Directors of either Steritech or Cerus or both, notwithstanding the
approval of this Merger Agreement by the shareholders of Steritech or Cerus or
the prior filing of this Merger Agreement with the Secretary of State of the
State of Delaware, or the consummation of the Merger may be deferred for a
reasonable period of time if, in the opinion of the Boards of Directors of
Steritech and Cerus, such action would be in the best interests of such
corporations. In the event of termination of this Merger Agreement, this Merger
Agreement shall become void and of no effect and there shall be no liability on
the part of either Constituent Corporation or its Board of Directors or
shareholders with respect thereto, except that Steritech shall pay all expenses
incurred in connection with the Merger or in respect of this Merger Agreement or
relating thereto.

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                  (E) COUNTERPARTS. In order to facilitate the filing and
recording of this Merger Agreement, the same may be executed in any number of
counterparts, each of which shall be deemed to be an original.

                  IN WITNESS WHEREOF, this Merger Agreement, having first been
fully approved by the Board of Directors of Steritech and Cerus, is hereby
executed on behalf of each said corporation and attested by their respective
officers thereunto duly authorized.


                                         STERITECH, INC.
ATTEST:                                  a California corporation


- ----------------------------------      By:____________________________________
Lori Roll                                   Stephen T. Isaacs
Secretary                                   President and
                                            Chief Executive Officer


                                       CERUS CORPORATION

ATTEST:                                a Delaware corporation

                                     
- ----------------------------------     By:_____________________________________
Lori Roll                                 Stephen T. Isaacs
Secretary                                 President and
                                          Chief Executive Officer

                                       5.
