Four women used polysiloxane contraceptive rings (CVR) impregnated with d-Norgestrel and estradiol for contraceptive purposes. The treatment was given in three-week cycles, leaving one treatment-free week between the cycles. Subjects were followed by blood sampling twice a week for three or four treatment cycles. Plasma concentrations of d-Norgestrel, estradiol, progesterone, and gonadotropins were determined by radioimmunoassay. The bleeding patterns were very acceptable. One subject experienced acne and weight gain, but no other side-effects were observed. Furthermore, no local irritation was found during the follow-up period of six or seven months. The individual variation in the mean plasma concentrations of d-norgestrel was between 3.2 and 1.1 ng/ml. Apart from one case, the highest individual levels were observed at the beginning of the first treatment cycle. Plasma estradiol was low during the treatment, but in some cases low post-insertion peaks were observed. No ovulatory progesterone values were found. Plasma LH was generally suppressed, but FSH was not. During the treatment-free week increasing concentrations of both LH and FSH were found, indicating an activation of pituitary function.