AMENDMENT NO. 5 TO LOAN AGREEMENT

This Amendment No. 5 to Loan Agreement ("Amendment") is made as of ___________,
1997 between Dow AgroScience LLC, formerly known as DowElanco LLC, a Delaware
limited liability company (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, 
Amendment No. 2 as of November 14, 1997, Amendment No. 3 as of November 18, 
1997, and Amendment No. 4 as of April 6, 1998 (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:

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

     1.2  Repayment

          (a)  The unpaid principal amount of each Advance shall be due and 
               payable on the Repayment Date.

          (b)  Interest on the unpaid principal amount of the Loan is due and 
               payable as it accrues on the first Business Day of each 
               calendar quarter until December 31, 1997; thereafter, interest 
               on the unpaid principal amount of the Loan shall be 
               capitalized and added to the unpaid principal amount of the 
               Loan on the first Business Day of each month.  Notwithstanding 
               the foregoing, all accrued and unpaid interest is due and 
               payable on the Repayment Date.

          (c)  Repayment may be made at any time, provided that the final 
               repayment be made on or prior to the Repayment Date.  Borrower
               must receive Lender's request for repayment by 9:00 a.m. Eastern
               Standard Time on any Business Day if repayment is to be made 
               that day.

2.   Section 1.5 Interest is hereby deleted in its entirety and replaced with 
the following:

     1.5  Interest

          (a)  The Loan shall bear interest from day to day at an interest 
               rate per annum

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               (i)    From October 1, 1997 through March 31, 1998, equal to 
                      LIBOR, as defined below, plus 0.25%, and

               (ii)   From April 1, 1998, until the Repayment Date equal to 
                      LIBOR, as defined below, plus 0.375%.

               (iii)  From October 1, 1997 until December 31, 1997, "LIBOR" 
                      means the rate of deposits in U.S. dollars for a period 
                      of three months which appears on the Telerate page 3750 
                      as of 11:00 a.m., London time, on the date that is two 
                      Business days prior to the first day of the Interest 
                      Period.  Effective January 1, 1998, "LIBOR" means the 
                      rate for deposits in U.S. dollars for a period of one 
                      month which appears on the Telerate Page 3750 as of 
                      11:00 a.m., London time, on the date that is two 
                      Business Days prior to the first date of the Interest 
                      Period.  Interest accrues on the unpaid principal amount
                      of each Advance from the date of each Advance and is 
                      payable in accordance with Section 1.2.

          (b)  The Interest Rate for each Interest Period is calculated by 
               Lender prior to each Interest Period.  Such calculation is 
               conclusive and binding absent manifest error.

          (c)  Interest is calculated on the basis of a 360-day year for 
               actual days occurring during the Interest Period.

          (d)  "Interest Period" means each calendar quarter, or part of each 
               calendar quarter, during which the Loan or any Advance is 
               outstanding between the date of this Amendment and December 
               31, 1997.  Thereafter, "Interest Period" means the period 
               commencing on the first Business Day of each month and ending 
               on the day immediately preceding the first Business Day of 
               the succeeding month.

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

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

LENDER:                                BORROWER:

Dow AgroSciences LLC                   Mycogen Corporation


By:  /s/ Sean S. Skinner               By:  /s/ J.A. Baumker
   ----------------------------           ----------------------------
Printed:  Sean S. Skinner              Printed:  J.A. Baumker
        -----------------------                -----------------------
Title:  Treasurer                      Title:  CEO
      -------------------------              -------------------------
Date:  4/13/98                         Date:  4/15/98
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