Inhibin B is comprised of two dissimilar disulfide-linked subunits, termed alpha and betaB, and is physiologically more important than inhibin A in the male. The aim of this study was to investigate testicular expression of inhibin subtypes in infertile men to uncover any interaction between Sertoli cells and germ cells. Ten azoospermic patients with Sertoli cell only syndrome (SCO) and 39 oligozoospermic men were included in this study. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone concentrations were determined by chemiluminescence assays. The serum concentrations of inhibin B were measured by enzyme-linked immunosorbent assay. Immunohistochemical staining for the alpha-subunit, betaA-subunit, and betaB-subunit of inhibin were performed on testicular biopsy specimens. The results were that serum inhibin B was undetectable in azoospermic men with SCO, while it was 133.8 +/- 82.0 pg/ml in oligozoospermic men. There was little expression of betaA in the testes of any patient. Expression of inhibin alpha and betaB was observed in Sertoli cells. The percentage of Sertoli cells expressing inhibin alpha was similar in azoospermic patients with SCO (55.3% +/- 20.6%) and in oligozoospermic patients (42.8% +/- 30.4%). In contrast, expression of betaB in Sertoli cells of azoospermic patients (24.9% +/- 16.8%) was lower than in oligozoospermic men (43.4% +/- 25.5%: P = 0.0308). There are no significant correlations between testicular expression of inhibin betaB and the serum inhibin B concentrations. The expression of inhibin betaB by Sertoli cells is dependent on the coexistence of spermatogenic activity within these seminiferous tubules, explaining why the level of inhibin B is low in patients with SCO.