Abstract Ovarian function, bleeding patterns and serum lipoproteins were studied in women using contraceptive vaginal rings (CVRs) of dimethyl-polysiloxane impregnated with steroids. The different CVRs were used for about 10 cycles each. The following groups were studied, with the daily steroid dosage given in parentheses. 1. 1. Women using CVRs delivering levonorgestrel (290 μg), norethisterone (850 μg), medroxyprogesterone acetate (700 μg) or megestrol acetate (1.9 mg), all of which were in combination with estradiol (200 μg). 2. 2. Women using CVRs delivering progesterone (5.2 mg). 3. 3. Women taking megestrol acetate orally (15 mg/day) for three weeks. In all women except those using the levonorgestrel CVR, there were indications of incomplete suppression of ovarian activity as shown by elevated levels of progesterone and/or estradiol peaks. Bleeding control seemed to be good with the levonorgestrel CVR and rather poor with the others. Levonorgestrel treatment was associated with a decrease in high density lipoprotein cholesterol (32%) and triglycerides (25%) and a 16% decrease in apolipoprotein A-I. Norethisterone induduced a 10% decrease in A-I and a reduction of cholesterol in very low density lipoprotein. All other lipid and apolipoprotein B, A-I and A-II values were unaltered with the administration of the CVRs and with oral megestrol acetate. Levonorgestrel was given in a higher dose than the other progestins, but the absence of effects of the high oral dose of megestrol acetate on the serum lipoproteins indicates that the progesterone-derived progestins in adequate doses probably would not alter the lipoprotein metabolism. Higher doses of progestins are needed to achieve acceptable control of ovarian activity and bleeding patterns than seen with these CVRs.