The presence of pyruvate decarboxylase activity has been demonstrated in Aspergillus nidulans, and a gene encoding a pyruvate decarboxylase has been isolated from this organism and physically characterized. The isolation of the pdcA gene in A. nidulans confirms the existence of the alcoholic fermentation pathway in this fungus, despite it being an obligate aerobic organism. Southern analysis showed that it is most probably a single copy gene. Several potential binding sites for a GATAR-binding protein were identified in the sequence just prior to the start point of transcription, and mutant alleles of the GATAR-binding protein-encoding gene, areA, affected pdcA mRNA levels in a manner that suggested that it influences pdcA expression in nitrogen repressing conditions. Other previously reported cases of AREA action are in nitrogen-limiting conditions. Interestingly, the production of ethanol was affected in a similar way by the same areA alleles, suggesting that changes in pdcA mRNA level are reflected in the changes in the level of ethanol production. The experiments presented here confirm that PDC levels are a major determinant of ethanol production under these conditions.