The incorporation of various potential intermediates into versicolorin A by a versicolorin A-accumulating mutant of Aspergillus parasiticus was studied. Both whole mycelium and cell-free extracts of this mutant were able to convert 14C-labeled versiconal hemiacetal acetate to versicolorin A. By the use of a labeled double substrate technique it was shown that two other compounds, versicolorin A hemiacetal and its acetate derivative, were also converted to versicolorin A. It is concluded that one or both of these compounds are intermediates in the biosynthesis of versicolorin A and therefore may possibly be involved in the biogenesis of the aflatoxins.