Ethinylestradiol (EE), at a dosage of 5 mg/day for 5 consecutive days (5 mg EE), has generally been used for interception. A combination of 200 micrograms EE and 2 mg dl-norgestrel (EE + NG) was proposed as an effective alternative. Efficacy and tolerance of these methods were compared in a randomized, double-blind study. A group of 465 women was studied with a follow-up rate of 94.3%. In the 5 mg EE group a pregnancy rate of 0.9% was observed, and in the EE + NG group a rate of 0.4% was found. These rates differ significantly from the expected rates (P less than 0.0005, in both series). Nausea was noted in 59.1% of the 5 mg EE group and in 54.0% of the EE + NG series. Nausea and vomiting occurred in 20.8% and 15.8%, respectively. The efficacy of both methods as alternative morning-after medication was confirmed. The new method is preferable because treatment is limited to only 1 day.