Thirty-one patients who underwent retropubic prostatectomy under epidural anesthesia for benign hypertrophy of the prostate were checked for serum prolactin levels before and during operation. A significant increase in serum prolactin levels was noted during operation after the removal of the prostate, as compared with levels just prior to its removal. This difference suggests high concentration of prolactin in the prostatic tissue, part of which was released into the bloodstream during the traumatic squeezing of the prostate.