
<PAGE>
 
                                                                   EXHIBIT 99.4
 
                                 ASHLAND INC.
 
                             OFFER TO EXCHANGE ITS
                         6 5/8% SENIOR NOTES DUE 2008,
         WHICH HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
                    FOR UP TO $150,000,000 PRINCIPAL AMOUNT
                              OF ITS OUTSTANDING
                         6 5/8% SENIOR NOTES DUE 2008
 
To Our Clients:
 
  Enclosed for your consideration is a Prospectus, dated       , 1998 (the
"Prospectus"), and the enclosed Letter of Transmittal (the "Letter of
Transmittal"), relating to the offer (the "Exchange Offer") of Ashland Inc.
(the "Company") to exchange its registered 6 5/8% Senior Notes Due 2008 (the
"New Notes") for up to $150,000,000 principal amount of its outstanding 6 5/8%
Senior Notes Due 2008 (the "Old Notes"), upon the terms and subject to the
conditions described in the Prospectus. The Exchange Offer is being made in
order to satisfy certain obligations of the Company contained in the
Registration Rights Agreement dated as of February 17, 1998, between the
Company and the Initial Purchasers.
 
  This material is being forwarded to you as the beneficial owner of the Old
Notes carried to us in your account but not registered in your name. A TENDER
OF SUCH OLD NOTES MAY ONLY BE MADE BY US AS THE HOLDER OF RECORD AND PURSUANT
TO YOUR INSTRUCTIONS.
 
  Accordingly, we request instructions as to whether you wish us to tender on
your behalf the Old Notes held by us for your account, pursuant to the terms
and conditions set forth in the enclosed Prospectus and Letter of Transmittal.
 
  Your instructions should be forwarded to us as promptly as possible in order
to permit us to tender the Old Notes on your behalf in accordance with the
provisions of the Exchange Offer. The Exchange Offer will expire at 5:00 p.m.,
New York City time, on       , 1998, (the "Expiration Date") (20 business days
following the commencement of the Exchange Offer) unless extended by the
Company. Any Old Notes tendered pursuant to the Exchange Offer may be
withdrawn at any time before 5:00 p.m., New York City time, on the Expiration
Date.
 
  Your attention is directed to the following:
 
    1. The Exchange Offer is for any and all Old Notes.
 
    2. The Exchange Offer is subject to certain conditions set forth in the
     Prospectus in the section captioned "The Exchange Offer--Conditions to
     the Exchange Offer."
 
    3. The Exchange Offer expires at 5:00 p.m., New York City time, on the
     Expiration Date, unless extended by the Company.
 
  If you wish to have the tender your Old Notes, please so instruct us by
completing, executing and returning to us the instruction form on the back of
this letter. THE LETTER OF TRANSMITTAL IS FURNISHED TO YOU FOR INFORMATION
ONLY AND MAY NOT BE USED DIRECTLY BY YOU TO TENDER OLD NOTES.
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                         INSTRUCTIONS WITH RESPECT TO
                              THE EXCHANGE OFFER
 
  The undersigned acknowledge(s) receipt of your letter and the enclosed
material referred to therein relating to the Exchange Offer made by Ashland
Inc. with respect to its Old Notes.
 
  This will instruct you to tender the Old Notes held by you for the account
of the undersigned, upon and subject to terms and conditions set forth in the
Prospectus and the related Letter of Transmittal.
 
  Please tender the Old Notes held by you for my account as indicated below:
 
                                            AGGREGATE PRINCIPAL AMOUNT OF OLD
                                                          NOTES
 
6 5/8% Senior Notes Due 2008.........     _____________________________________
 
[_]Please do not tender any Old
   Notes held by you for my account.
 
Dated: _______________________ , 1998     _____________________________________
 
                                          _____________________________________
                                                       SIGNATURE(S)
 
                                          _____________________________________
 
                                          _____________________________________
 
                                          _____________________________________
                                                PLEASE PRINT NAME(S) HERE
 
                                          _____________________________________
 
                                          _____________________________________
                                                       ADDRESS(ES)
 
                                          _____________________________________
                                           AREA CODE(S) AND TELEPHONE NUMBER(S)
 
                                          _____________________________________
                                              TAX IDENTIFICATION OR SOCIAL
                                                     SECURITY NO(S).
 
  None of the Old Notes held by us for your account will be tendered unless we
receive written instructions from you to do so. Unless a specific contrary
instruction is given in the space provided, your signature(s) hereon shall
constitute an instruction to us to tender all the Old Notes held by us for
your account.
