Eggs of 2 strains of D. melanogaster, Florida-9, which is sensitive to aflatoxin B1 (AFB1)(I) [1162-65-8] and strain Lausanne-S which is not, were deposited on medium containing either low or high doses of dietary aflatoxin G1 [1165-39-5], aflatoxin B2 (AFB2) [7220-81-7], or sterigmatocystin (ST) [10048-13-2] and allowed to develop into 2nd instar larvae, which were transferred onto medium containing either high or low doses of dietary AFB1 (posttreatment) and allowed to complete development and eclose as adults.Viability and development data were analyzed to determine the effects of the various pretreatments on the level of AFB1-induced toxicity in the posttreatments.In no case did any of the pretreatments reduce the toxic effects of AFB1 posttreatment responses.However, for strain Florida-9, all high-dose pretreatments resulted in enhanced posttreatment toxicity, and all low-dose pretreatments also enhanced toxicity of high-dose posttreatments.For strain Lausanne-S, high-dose AFB2 pretreatment significantly enhanced toxicity of both high- and low-dose posttreatments.Thus, in strain Florida-9, pretreatment with relatively less toxic mycotoxins (ST and AFB2) has an enhancing effect on AFB1-induced toxicity, whereas in strain Lausanne-S, a similar but smaller enhancing effect is seen only with AFB2 pretreatment.