Technical Abstract: To date the sexual stages or teleomorphs have been described for three aflatoxigenic species in Aspergillus section Flavi: Petromyces flavus, P. parasiticus and P. nomius. In this study we examined the possibility of interspecific matings between A. flavus and A. parasiticus. These species can be distinguished morphologically and genetically, as well as functionally via the biosynthesis of specific aflatoxins and an unrelated mycotoxin, cyclopiazonic acid (CPA). A. flavus produces both B aflatoxins and CPA, B aflatoxins or CPA alone, or neither mycotoxin; A. parasiticus produces B and G aflatoxins or O-methylsterigmatocystin but not CPA. Only four out of forty-five attempted interspecific crosses between compatible mating types of A. flavus and A. parasiticus were fertile. Single ascospore strains from each cross were isolated and shown to be hybrids using array comparative genome hybridization and multilocus sequence typing. Higher mean concentrations of B1, B2, G1 and G2 aflatoxins, and CPA in the F1 progeny compared to midpoint parent toxin levels indicate high heritability of these toxins and possibly hybrid heterosis.