It is demonstrated that, in fungal cells grown in synthetic media, the Apyap1 gene is implicated in the modulation of aflatoxin biosynthesis following the perturbation of redox balance. This study suggests that an association between oxidative stress and aflatoxin biosynthesis also occurs in maize seeds. We used DeltaApyap1, a strain in which the gene Apyap1 was disrupted, to verify whether this oxidative stress-related transcription factor, by affecting cell redox balance, can have a role in the modulation of aflatoxin synthesis. The amount of hydroperoxides (ROOH) produced by wild type (WT) and DeltaApyap1, both grown in potato dextrose broth, was assayed in the filtrate. In maize seeds (30 g), inoculated with WT and DeltaApyap1conidia and incubated at 30 degrees C for 15 days, lipoxygenase activity (LOX), lipoperoxides (LOOH) production, fungal growth and aflatoxin biosynthesis was analysed. It was observed that DeltaApyap1 released more hydroperoxides in the culture media and more aflatoxins in seeds, possibly through stronger stimulation of LOX, which, in turn led to greater LOOH production in the seeds. On the basis of the results, a hypothesis regarding strategies to control aflatoxin synthesis is formulated.