Radioimmunoassay for prostatic acid phosphatase and a conventional enzymatic method using alpha-naphthyl phosphate were employed to document the changes in serum levels of this enzyme following transurethral prostatectomy and prostatic massage. Thirty-four patients with histologically proved benign prostatic hyperplasia and 120 controls were studied. Consistent parallel elevations were noted after surgical trauma. A rapid clearance was observed with normal levels returning at twenty-four hours. Prostatic massage did not elicit a change by either method.