PIP: 20 women with metabolic, vascular, or gynecoendocrinological contraindications to use of combined oral contraceptives (OCs) or norsteroid progestins participated in a 6-month study of chlormadinone acetate, a progestin derived from 17-OH progesterone known for its weak androgenic activity. 5 mg doses of chlormadinone acetate were administered on the morning and evening of the 6th to the 26th cycle day for 3 woman and on the 8th to the 26th cycle day for 17 others. Blood tests were conducted during the luteal phase after fasting. The average age of the study subjects was 29.9, the average weight was 57.8 kg, and the average height was 161 cm. There were no significant variations over the course of the study in weight, blood pressure, renin substrate, high density lipoprotein (HDL) cholesterol, triglycerides, plasma apo-B, or antithrombin III. There was a significant reduction in apoprotein A1, the principle protein fraction of high density lipoproteins, from the 3rd to the 6th cycles, and a nonsignificant reduction of the apoprotein B. The ratio of A1/B apoproteins was not significantly modified. There were no signs of hyperestrogenism, hyperandrogenic effects, or digestive intolerance. In most cases there was no significant change in cycle duration or intensity of menstrual bleeding. 3 patients were recurrently amenorrheic. The amount of bleeding was considered normal by 14 patients and diminished by 3. There were no cases of menorrhagia and 5 of minor metrorrhagia in the first 3 months of use. No pregnancies occurred. After voluntary termination of contraception, 2 patients rapidly became pregnant. Measurement of ovarian hormone levels and gonadotropins indicated that chlormadinone acetate at the prescribed dose completely inhibited progesterone secretion in all patients and considerably reduced the production of estradiol in the luteal phase. Chlormadinone acetate has the dual advantages of avoiding the estrogen-induced side effects of combined OCs and avoiding hyperestrogenism. The use of a progestin derived from 17-OH progesterone may offer a contraceptive method suitable for women with metabolic or vascular contraindications to combined OCs or gynecoendocrinological contraindications to low dose progestins, who are unable or unwilling to use mechanical or local contraceptives. Chlormadinone acetate should however remain a method for use under exceptional circumstances.