The events of 1999 highlight the importance of the need for identity preservation (IP) of products that result from genetic modification. In April of 1999, Archer Daniels Midland Co. and A. E. Staley Co. announced that they would not accept product that was not approved for export to the European Union. By the time the 1999 harvest arrived, decision makers in the grain marketing industry realized the nature of their business had dramatically changed in just one growing season. In particular, they needed to preserve the identity of all grains and oilseeds intended for European and Japanese markets. During the remainder of the 1999 growing season, consumer concern about the safety of genetically modified organisms (GMOs) increased. The need for IP represents a substantial challenge for the grain marketing system, since the system has evolved over time to handle large volumes of homogeneous product. The objective of this study is to examine the impact of IP for GMOs on the grain handling system for a typical region in the eastern corn belt.