The nucleotide sequence of a 1.5-kb fragment of the promoter region of the Aspergillus oryzae agdA gene encoding alpha-glucosidase was determined. A comparison with the promoter regions of other Aspergillus amylase genes indicated that there are three highly conserved sequences, designated Regions I, II and III, located at -670 nt, -596 nt and -544 nt relative to the start codon, respectively. The function of these consensus sequences in the agdA promoter was investigated by deletion analysis of a promoter fusion with the Escherichia coli uidA gene, using the niaD homologous-transformation system. Deletion of the upstream half of Region III (IIIa; -544 to -529) resulted in a more than 90% reduction in GUS activity and abolished maltose induction, suggesting that Region IIIa is a functionally essential element for high-level expression and maltose induction. Deletion of Region I and the downstream half of Region III (IIIb; -521 to -511) resulted in a significant reduction in GUS activity, but did not affect maltose induction. This suggested that these two elements most likely contain sequences involved in efficient expression in cooperation with Region IIIa. In addition, deletion of a 340-bp region between Region IIIb and the putative TATA box resulted in a 2-fold increase in activity.