A clinical investigation was carried out to analyze the frequency of elevated serum acid phosphatase (SAP) levels after ejaculation and needle biopsy of the prostate gland. Major mechanical manipulative procedures such as needle biopsy caused marked acute elevations in SAP levels but return to normal within twenty-four hours. It is demonstrated that SAP levels remained essentially unchanged after ejaculation. It has been previously shown that procedures such as prostatic massage, catheterization, and endoscopic examination normally do not elicit abnormal SAP levels. Hence any elevation of SAP warrants further evaluation for serious urologic disease.