To identify downstream and/or interactive factors of the nsdD gene, which encodes a positive regulator of sexual development of Aspergillus nidulans, suppressor mutants displaying a self-fertile phenotype were isolated from a sterile nsdD deletion mutant. At least five different loci (sndA-E) were identified and genetically analyzed. In the nsdD (+) background, most of the suppressors showed a marked increment of sexual development, even under the stress conditions that normally inhibited sexual development. The common phenotype of the suppressor mutants suggested the involvement of the snd genes in the negative regulation of sexual development in response to the environmental factors.