Inhibin is a gonadal hormone involved in the non-steroidal regulation of follicle stimulating hormone (FSH) secretion. Using the cDNAs coding for bovine inhibin A and B subunits we have identified inhibin genes within the human genome using Southern blot hybridisation techniques. The genes are likely to he present as single copies. Cloning and sequencing inhibin genes obtained from lambda libraries of human genomic DNA provide structural and sequence data on the human A and B genes. Comparison of the known inhibin gene sequences showed, in particular, that the B subunits have identical sequences in man, pigs and cattle thus demonstrating a remarkable evolutionary conservation in these genes.