Part of the nucleotide sequence of the ver-1 homolog in each of two strains of Aspergillus oryzae, Aspergillus sojae, and Aspergillus flavus were compared with two homologs in Aspergillus parasiticus. The homologs in A. oryzae and A. sojae (non-aflatoxin-producers) exhibited an extremely high degree (93.8-99.8% for A. oryzae : and 96.0-99.5% for A. sojae) of sequence identity with that of A. flavus and A. parasiticus. No two strains within the same species, except A. sojae, were identical. No sequence fingerprint was found to distinguish between A. oryzae and A. flavus, or between A. sojae and A. parasiticus. The predicted partial amino acid sequences (181 amino acids) of the ver-1 homologs had at most two amino acid changes relative to A. par asiticus SYS-4 ver-1. Transcripts of ver-1 homologs in the strains of A. oryzae and A. sojae examined were not detected by the polymerase chain reaction coupled with reverse transcription. By Southern analysis, a total of 46 strains of A. oryzae were examined for the presence of the ver-1 homolog. The homolog was detected in 38 strains, but not in 8 strains. Morphologically, strains with and without the ver-1 homolog were indistinguishable. Thus, A. oryzae contains strains with and without a homolog of the aflatoxin biosynthetic gene ver-1.