Prostatic function is most accurately represented by it s fluid. Using dogs as experimental animal, prostatic fluid was collected trans-urethrally by the Huggins' method, and the amount of fluid secreted, protein content and fructose level were measured in nontreated dogs and sexual hormone treated dogs. 1) Concerning the amount of fluid se c reted after single stimulation with pilocarpine hydrochloride 78.3 to 92.5% of the total secretion was collected within the first 1 hour. The 1 hour fluid showed monophasic or diphasic patterns. With multiple stimulations, the amount of fluid secreted was gradually decreased, while the resting fluid showed less differences. 2) The protein content of the fluid secreted was 565mg/dl as an average. I n the 1 hour fluid showed highest content in the fluid collected within 10 minutes, followed by a rapid decrease until in 30 minutes when the decrease became slowly. By means, of electrophoresis, fractions were demonstrated at the 0- and 7-globulin sites of the serum which were called as I and II fractions respectively with averages of 45.3% and 54.7% of the total. Glycoproteins were recognized 52.4% in the I fraction and 47.6% in the H fractions. No lipoprotein was demonstrated. 3 ) Fructose content was 4.3mg/dl as an average. Change in its content by time in the 1 hour fluid showed gradual decrease of slight degree. 4) With administration of androgen, amoun t of fluid secreted and protein and fructose contents were all increased. Electrophoretically, both of the protein and glycoprotein were risen in the I-fraction. The maximum effect in amount of fluid was achieved with daily administration of 5 to 10 mg of TP, but the protein and fructose levels showed no remarkable difference with the dose of administration. 5) Inverse results were obtai n ed with administration of estrogen. Combined treatment with the ratio of the androgen and estrogen at 20 : 1 resulted a dominant effect of estrogen with decreased amount of fluid, while it was unchanged with the ratio at 30 : 1. 6) With castration, the amount of fluid decreased in all dogs studied down to less than 1 cc within 10 days, which was recovered with administration of TP at the dose of 20mg daily as the maximum effect. The protein and fructose levels were also brought back.