Levonorgestrel and estradiol releasing contraceptive vaginal rings (CVR) with an outer diameter of 50 mm were used by twenty women. The treatment was given in three-week cycles followed by one treatment-free week. The treatment was planned to cover six cycles. All subjects kept records of bleeding and were controlled clinically in the course of treatment. Three subjects were followed by blood sampling. Plasma levonorgestrel, estradiol, progesterone and gonadotropins were determined. The subjects experienced no difficulties in using the CVR and 90 per cent continued the treatment through the whole experimental period of six months. One subject discontinued after three cycles because of irregular bleedings and one subject after five cycles because of urinary discomfort. Regular bleedings were observed only in three subjects and in nine cases the bleeding started with the CVR in situ during the last days of the three-week treatment period. Breakthrough bleeding occurred in the remaining eight subjects. The subjective side-effects were as follows: weight gain in four subjects, oedema in one subject and urinary discomfort in one subject. Pituitary function was not generally suppressed as judged by plasma gonadotropins. Out of the three subjects studied, two experienced ovulatory plasma progesterone concentrations.