Aspergillus flavus is similar to many filamentous fungi in that it has multinucleate mycelium. It differs from A. nidulans in that the conidia are multinucleate as well. The ontogeny and function of multiple nuclei in the conidium and their role in the ecology of the fungus are unknown. A heterokaryotic or diploid nuclear condition could serve as a source of genetic diversity within strains for pathogenicity and aflatoxin production. We are using two nuclear localized fluorescent reporter constructs to track nuclei and their active migration during conidial formation and in response to environmental stressors.