1. High concentrations (272 ± 33 ng/ml) of urogastrone-epidermal growth factor were measured in prostatic fluid from normal males by a specific radioimmunoassay.
2. Significantly lower concentrations (155 ± 24 ng/ml) were observed in the prostatic fluid of patients with benign prostatic hypertrophy than in the age-matched normal controls (2P < 0.01).
3. The growth factor content of seminal fluid was accounted for by the contribution of prostatic fluid.
4. Immunochemical studies failed to show evidence of synthesis within the gland nor could high affinity receptors for the protein be demonstrated in membrane preparations of the gland.