Changes in messenger ribonucleic acids (mRNAs) of human testicular inhibin alpha and beta B subunits induced by human menopausal gonadotropin (hMG) and human chorionic gonadotropin (hCG) were assessed in vivo and in vitro. After a single administration of hMG, inhibin alpha mRNA in the human testis significantly increased, whereas inhibin beta B mRNA remained unchanged. Administration of hCG induced a slight increase in inhibin alpha mRNA without affecting inhibin beta B mRNA. In experiments in vitro using the testicular organ culture technique, an exposure to hMG for 24 hours induced a dose-related significant increase in inhibin alpha mRNA. Inhibin beta B mRNA was not affected by either hCG or hMG exposure. These results indicate that luteinizing hormone (hCG) as well as follicle stimulating hormone (hMG) may play a role in the regulation of human testicular inhibin alpha mRNA, although the mechanism of the LH action is not clear.