Twenty-two hypertrophied prostates removed in surgery were checked for prolactin concentration by the radioimmunoassay method. The mean concentration in the prostatic tissue was found to be 38.2 +/- 1.9 ng./Gm. while the mean basal serum level was 11.9 +/- 1.3 ng./ml. It is concluded that serum prolactin levels do not reflect prostatic prolactin concentration. The possibility that interrelationship in action exists between androgens and prolactin affecting each other's concentration, both influencing prostatic metabolism is discussed.