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                        DEKALB GENETICS CORPORATION LOGO
 
                                  May 15, 1998
 
    Fellow Shareholders:
 
     We are pleased to inform you that DEKALB Genetics Corporation has entered
into an Agreement and Plan of Merger with Monsanto Company, pursuant to which a
wholly owned subsidiary of Monsanto has commenced a tender offer to purchase all
of the outstanding shares of Class A and Class B Common Stock of DEKALB for $100
per share in cash. The tender offer will be followed by a merger in which any
shares of Class A or Class B Common Stock not tendered pursuant to the tender
offer will receive $100 per share in cash or the highest price paid per share
pursuant to the tender offer. As a result of the merger, DEKALB will become a
wholly owned subsidiary of Monsanto.
 
     The Board of Directors of DEKALB has determined that the Monsanto tender
offer and the merger are fair to and in the best interests of DEKALB and its
shareholders and recommends that shareholders accept the Monsanto offer and
tender their shares of Common Stock pursuant to it.
 
     Enclosed are the Monsanto Offer to Purchase, dated May 15, 1998, Letter of
Transmittal and other related documents. These documents set forth the terms and
conditions of the tender offer. Attached is a copy of the Company's Schedule
14D-9, as filed with the Securities and Exchange Commission. The Schedule 14D-9
describes in more detail the reasons for the Board's conclusions and contains
other important information relating to the tender offer. We urge you to
consider this information carefully.
 
     The Board of Directors and the management and employees of DEKALB thank you
for your support.
 
                                          Sincerely,
 
                                          BRUCE P. BICKNER
 
                                          Bruce P. Bickner
                                          Chairman of the Board and
                                          Chief Executive Officer