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. 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.  We are examining the possibility of interspecific matings in experimental and natural populations.