We have recently purified a novel pituitary polypeptide designated 7B2. By raising polyclonal antibodies to a synthetic 7B2 fragment in rabbits, we have developed a sensitive and specific radioimmunoassay for this novel polypeptide, and it has been used for the study of the release of immunoreactive 7B2 from rat anterior pituitary cells in vitro. In addition, immunocytochemical study shows that 7B2 is present in the gonadotropin cells of rat anterior pituitary. The aim of the present studies is to investigate the effect of human β-inhibin, testosterone, and combined testosterone plus human β-inhibin on the induced release of immunoreactive 7B2, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) in rat anterior pituitary cell culture in vitro. Our results show that both human β-inhibin and testosterone effectively suppress the stimulatory effect of luteinizing hormone-releasing hormone (LHRH) on immunoreactive 7B2, FSH, and LH release. The present data indicate that the regulation of secretion of 7B2 and pituitary gonadotropins may be under a similar type of feedback mechanism.