Contraceptive efficacy, cycle control and side effects of two types of 0.75 mg levonorgestrel tablets taken postcoitally during the periovulatory period of one cycle were studied in a multicenter trial involving 361 women. No significant differences were found between the two types of levonorgestrel pills in terms of contraceptive efficacy, cycle control and side effects. The failure rate observed (1.4% per treated cycle) was similar to that reported for other hormonal approaches to emergency postcoital contraception. Intermenstrual bleeding or spotting occurred in 11.5% of the cycles and anovulation as assessed from BBT charts in 14.4% of cycles. One or more side effects were reported by 22.2% of subjects. The relatively frequent occurrence of cycle disturbances and subjective side effects make it unlikely that the repeated postcoital use of levonorgestrel would be an acceptable routine method of contraception for most women.