Medroxyprogesterone acetate (MPA) was administered, as a contraceptive, by intramuscular injection in doses of 150 mg every 90 days, or 300—150 mg every 180 days, to 5 women, over a period of 27 to 42 months. No major adverse reactions were reported, and the minor side elfects were only as frequent as those reported for oral contraceptives. The LH basal levels were depressed in all subjects; FSH and prolactin serum concentrations were within the range found in normally cycling women. Synthetic TRH released prolactin in 4 subjects, and the maximal response was within 10–20 minutes after TRH injection. In the fifth case there was no prolactin release.