In a double-blind randomized study suppression of ovarian activity effects on the cervix and endometrium menstrual bleeding patterns and overall tolerance were assessed during administration of two low-dose oral contraceptives: Eve 20 (20 mcg ethinyl estradiol (EE) and 500 mcg norethindrone) and Lovelle (20 mcg EE and 150 mcg desogestrel). 118 healthy women aged 18-25 years with comparable height weight and menstrual cycle were studied in 10 investigation centers while taking either Eve 20 (n = 59) or Lovelle (n = 59). During 3 treatment cycles ovarian activity was evaluated by sonographic determination of follicular size and by simultaneous assessment of serum endocrine profiles (LH FSH estradiol [E2] and progesterone [P]). Treatment cycles 4-6 served to evaluate the patterns of menstrual bleeding and the overall subjective tolerance of each contraceptive. While on the pills no ovarian activity was found in over 90% of all investigated cycles. Follicular activity and/or cyst formation were detected in 18 of 173 cycles (Eve 20) and in 5 of 175 cycles (Lovelle). Gonadotropin levels were suppressed (LH 5 nmol/l ovulation had presumably occurred in 4.1% (Eve 20) vs. 2.9% (Lovelle) of treatments. However when the sonographic and endocrinological data were combined no ovulation was documented in any treatment cycle. Both contraceptives were rated as good or very good by most subjects.