Adenylate cyclase activity was studied in Saccharomyces cerevisiae's cell division cycle (cdc) mutant 35-1. The temperature sensitive mutant cdc35-1 was previously mapped as an allele of cyr, the adenylate cyclase gene. However, the adenylate cyclase activities of membranes prepared from cdc35-1 were not thermosensitive. The adenylate cyclase activity of cdc35-1 was found to have an altered Mn2+ dependency and did not respond to Gpp(NH)p stimulation. These results suggest that cdc35-1 mutation may not be at the catalytic site but at a site where adenylate cyclase interacts with regulatory proteins.