Aspergillus flavus, the causal agent of aflatoxin contamination of cottonseed, is a complex species composed of many distinct vegetative compatibility groups. Isolates belonging to different vegetative compatibility groups may produce widely different quantities of aflatoxins. Some naturally occurring isolates of A. flavus produce no aflatoxins. Some of these atoxigenic strains have the ability to competitively exclude aflatoxin-producing strains during crop infection and thereby reduce aflatoxin contamination. In both greenhouse and field-plot tests atoxigenic strain efficacy has repeatedly been demonstrated. A. flavus communities resident in soils vary among agricultural fields in aflatoxin producing capacity. Field-plot tests suggested that applications of atoxigenic strains may provide long-term reductions in the aflatoxin producing potential of fungi resident in treated fields. Tests to evaluate the longevity of changes to A. flavus communities induced by atoxigenic strain applications were initiated in 1996 under an Experimental Use Permit (EUP) issued by the EPA. The experimental program outlined in the EUP called for treatments over a three year period (1120 acres total) and for monitoring the A. flavus community from 1996 through 1999. Different treatment regimes were applied to different fields with some fields receiving treatment only in a single year and others receiving treatments in multiple years.