Manufacturers have steadily been decreasing the amounts of estrogen and progestin in oral contraceptives (OCs) in an effort to enhance safety and tolerability while preserving contraceptive efficacy. A new formulation containing 20 microg ethinyl estradiol (EE) and 100 microg levonorgestrel (LNG)--representing the lowest available contraceptive dose of each hormone--has undergone extensive clinical testing in the United States and Germany. A total of 1590 women in 61 centers received 20 microg EE and 100 microg LNG for 6 cycles. Overall, 4 pregnancies possibly related to treatment failure were reported, reflecting an overall Pearl Index (number of pregnancies per 100 woman-years of treatment) of 0.65 and a failure rate of 0.34%. Cycle control was typical of low-dose OC use. Spotting and breakthrough bleeding occurred most commonly during the earlier cycles in each study. Adverse events were typical of those seen with OC use and led to study discontinuation in 6.6% of the women. Intermenstrual bleeding was the cause for early study withdrawal in 2.6% of women. The study results suggest that the combination of 20 microg EE and 100 microg LNG offers the benefits of low hormone content with good contraceptive efficacy, cycle control, and tolerability.