Contraceptive efficacy, subject acceptability (cycle control, side-effects, acne score and weight gain) and blood pressure of a monophasic oral contraceptive containing 30 mu g ethinyl estradiol plus 150 mu g desogestrel (Marvelon) were assessed in an open-label 6-cycle multicenter study in Argentina (7 centers) and Venezuela (5 centers). Of the 407 participating women, 389 (95.6%) completed six cycles of treatment, providing data for a total of 238 3 cycles. No pregnancies occurred during the course of the study, confirming the high contraceptive reliability of Marvelon. Cycle control was excellent the duration of withdrawal bleeding decreased during consecutive treatment cycles and the incidence of spotting and breakthrough bleeding was low. The desogestrel/ethinyl estradiol combination was well tolerated and the incidence of minor side-effects, which was already low in the first treatment cycle, in most cases decreased during the subsequent cycles. The preparation was effective in reducing pre-existing acne, whereas it did not induce clinically relevant changes in blood pressure and body weight. Marvelon was shown to provide effective oral contraception, with good tolerance and excellent cycle control in Latin-American women.