A spontaneous suppressor mutant, hah, which suppressed the colonial growth of adenylyl cyclase mutants (cr-1) was isolated. The morphology of cr-1 hah was filamentous, but slightly different from that of wild type on solid medium. The hah strain formed many high aerial hyphae, but did not form any conidia. The expression levels of an adenylyl cyclase gene, nac, in both hah and cr-1 hah were much higher than those in wild type or in cr-1. The level of cAMP in cr-1 was very low but returned to close to the wild-type level in the cr-1 hah suppressed strain, whereas that in the strain carrying hah alone was similar to or a little higher than that in wild type. The hah gene was located 13.3 map units from in1 on the right arm of the linkage group V. The hah mutation was recessive and allele specificity of hah for the suppression of cr-1 mutations was weak.