The localization and distribution of inhibin/activin subunits was evaluated in the testes of three nonhuman primate species (Macaca fascicularis, M. mulatta, M. arctoides), of young (31 to 43 years) and old (60 to 85 years) men, and of men with disturbed or arrested spermatogenesis using immunohistochemical techniques (peroxidase-anti-peroxidase and alkaline-phosphatase/anti-alkaline-phosphatase technique). Specific polyclonal (anti-porcine inhibin alpha-1-32 and anti-bovine activin A) and monoclonal (anti-human inhibin alpha-1-32 and anti-human activin beta A-82-114) antisera were employed. Among all nonhuman primate species and in men, inhibin/activin subunits were present in the cytoplasm of Sertoli cells and Leydig cells but not in germ cells. No relationship could be established between the staining pattern for inhibin/activin subunits and the completeness or the stage of the spermatogenic process. The staining for the beta A-subunit in Sertoli cells appeared more intense in the testes of old men compared with that of young men. The majority of Leydig cells contained either the alpha-subunit and beta A-subunit or the beta A-subunit alone. The signal for the beta A-subunit was remarkably intense in normal and hyperplastic human Leydig cells. These observations demonstrate the presence of inhibin/activin subunits in Sertoli cells and Leydig cells of adult primates and raise the possibility that these subunits or their respective dimers (inhibin A/activin A) might subserve a paracrine/autocrine role in the adult primate testis.(ABSTRACT TRUNCATED AT 250 WORDS)