In addition to kallikrein hK3, a serine protease generally reported as PSA (prostate-speci®c antigen), at least two other enzymes in human seminal plasma also cleave syn-thetic peptidyl substrates derived from the sequence of human semenogelins. We have identi®ed one of these as prostatic acid phosphatase (PAP), a major component of prostatic ¯uid whose physiological function is unclear.