Abstract: Four contraceptive steroids, Medroxyprogesterone acetate, Megestrol acetate, Chlormadinone, and Norethisterone were studied in experimental renal hypertensive rats.During the period of 7 to 21 days of treatment, a mild and gradually developing hypotensive effect was observed for all the four compounds administered subcutaneously alone or orally in combination With 17-ethinyl estradiol in doses approximating 400～800 times those used clinically on body weight basis. After withdrawal of the drugs the recovery of blood pressure was also gradual. The action of Megestrol acetate and Chlormadinone appeared to be the most potent, while that of Medroxyprogesterone acetate the least; but even with the strongest, the maximal depression of blood pressure was only 15% of the control value.Megestrol acetate or norethisterone injected subcutaneously to DOCA—induced hypertensive rats in doses as described above produced a similar but milder effect.When the dosage was decreased to 50 times that used clinically, the most potent member of this group—Megestrol acetate, taken orally with oestrogen for 21 days did not show any influence on the blood pressure of either renal hypertensive or normal rats.The significance of these observations was discussed.