The polymerase chain reaction (PCR) was used to detect several forms of adenylyl cyclase (AC's) expressed in human erythroleukemia (HEL) cells. Degenerate oligonucleotide primers were synthesized based on the conserved sequences in the C2a area of the AC's. HEL cells were found to contain mRNA for type III and type VI AC. In addition, a novel AC message was identified. The cloned sequence, excluding primer areas, represented 69 amino acids with most similarity to rat AC's II and IV. Northern analysis of RNA from HEL cells demonstrated a 6.7 kilobase message. RNase protection assays revealed that in HEL cells the novel AC mRNA was dominant compared to types III and VI. Human embryonic kidney cells (HEK293) were also used a source of mRNA to synthesize cDNA for PCR reactions. The HEK293 cells were found to contain message corresponding to type II, III, VI AC as well as the novel AC message. The novel AC message was also detected in human brain tissue and was most abundant in the caudate, cerebellum and hippocampus. The smallest amount of novel AC mRNA in the tested brain tissue was found in the cortex. The mRNA for the novel AC was relatively abundant in human liver.