Effects of pituitary, adrenal, anabolic, thyroid and anti t hyroid hormones on amount of fluid secreted and contents of protein and fructose in the prostatic fluid obtained transurethrally on the Huggins'dog were investigated. As a rule, the hormones were administered for a period of 20 days. 1) With admini stration of gonadotropic hormones at doses of 500 IU every thrid day, increases in amount of fluid were observed in the order of HCG, HCG to PG (10 : 1) and PMS. After discontinuing the administration, the amount of fluid in the dogs given such hormones decreased slowly compare to that of given TP.. Contents of protein and fructose in the fluid also showed an increase though the effect was not differed among the_gonadotropic hormones given. Electrophoretically an increase of the I fraction was recognized both for protein and glycoprotein. 2) With combined administration of gonadotropic and androgenic hormones, more striking increase in the amount of fluid was observed than with single administration of each hormone. There was no difference in the increase of protein and fructose contents between combined and single administration. 3) ACTH treatment resulted marked increase in the amount of fluid as well as moderate increases in the protein and fructose content around 20 days after the cessation of the administration. 4) With administration of prolactin, the amount of fluid was increased though the rate of increase was found to be the minimum compared to that of with TP, gonadotropic hormone and ACTH. The protein and fructose contents showed a slight increase. 5) A slight suppressive effect was observed with administration of cortisone on amount of fluid. Protein content was decreased and the I fraction was lowered. 6) No noticeable effect was seen after administration of an abolic hormone 4 Cl TA on the amount of fluid, while a slight promoting effect was observed on the protein and fructose contents of the fluid. 7) With administration of thyroid hormone, the amount of fluid was decreased and the content of fructose was lowered. Little effects were recognized with anti-thyroid hormone.