Analyses of the proteins of azoospermic ejaculates from subjects with defective seminal vesicles demonstrated that three prostatic-secreted proteins were predominant. Prostatic acid phosphatase (PAP), prostate-specific antigen (PSA; or gamma-seminoprotein), and beta-microseminoprotein (beta-MSP; or beta-inhibin), were identified as the three predominant proteins secreted by the normal human prostate gland. Immunohistochemical localization of these proteins, in the epithelium of normal prostatic acini and ducts, with the avidin-biotin complex procedure demonstrated that each PAP-immunoreactive cell was invariably immunoreactive both with PSA-and beta-MSP-monospecific antisera as well.