The differential localization of the inhibin beta subunits betaA and betaB in the testis of adult bull was studied using specific monoclonal and polyclonal primary antibodies. Inhibin betaA- and betaB-subunits were localized only in the Sertoli cells. The inhibin betaA-subunit was observed in the cytoplasm while the betaB-subunit was localized in the nucleus. No specific findings depending on spermatogenic stages were observed among the seminiferous tubules. Moreover, the inhibin alpha-subunit was not detected in the testis of the bulls. In addition, no inhibin subunits were detected in the Leydig cells and spermatogenic cells. These findings indicate the presence of betaA- and betaB-subunits in the bull, which may suggest a possibility that activin is produced and/or stored in the Sertoli cells and regulates spermatogenesis in an autocrine/paracrine manner. Moreover, the inhibin betaB-subunit may be produced in the nucleus but the functional meaning of this is not yet clear.