Growth and aflatoxin production of Aspergillus flavus in preharvest maize grown in Texas, USA in 1989 were determined after treatment with chitosan, Bacillus subtilis and Trichoderma harzianum. Individual or combined control treatments were applied at the milk stage of ear development, 48 h before or after kernel inoculation with an aflatoxigenic isolate of A. flavus. Single and combined treatments reduced A. flavus growth and aflatoxin production. Toxin accumulation was significantly (P < 0·05) reduced, in some instances to non-detectable concentrations by single pretreatments. Either B. subtilis or chitosan as independent treatments applied 48 h before inoculation with A. flavus inhibited aflatoxin production.