AMENDMENT NO. 3 TO LOAN AGREEMENT

This Amendment No. 3 to Loan Agreement ("Amendment") is made as of November 
18, 1997 between DowElanco LLC, a Delaware corporation, f/k/a DowElanco, an 
Indiana general partnership (the "Lender"), and Mycogen Corporation, a 
California corporation (the "Borrower") (together, the "parties").

WHEREAS, Lender and Borrower are parties to that certain Loan Agreement dated 
as of April 1, 1997, as amended by Amendment No. 1 as of September 29, 1997, 
and Amendment No. 2 as of November 14, 1997 (the "Agreement"); and

WHEREAS, the parties wish to further amend the Agreement;

NOW THEREFORE, the parties hereto have agreed and do hereby agree to amend the 
Agreement as follows:

     Section 1.2 is hereby deleted in its entirety and replaced with the      
following:

     1.2 Repayment

         Repayment may be made at any time, provided that the final repayment 
         be made on or prior to September 30, 1998.

     All other terms and conditions of the Agreement shall remain in full 
     force and effect.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly 
executed on the date first written above.

LENDER:                                  BORROWER:

DowElanco LLC                            Mycogen Corporation


By: /s/ Sean S. Skinner                  By: /s/ James A. Baumker
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Printed: Sean S. Skinner                    Printed: James A. Baumker
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Title: Treasurer                            Title: VP CFO
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Date: 11/18/97                               Date: 11/19/97
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