Fifty eight fertile female volunteers between 20 to 45 years were enrolled in a clinical trial to evaluate the efficacy and tolerance of the progestin dienogest (17 alpha-cyanomethyl-17 beta-hydroxyestra-4,9-dien-3-one, VEB Jenapharm Jena GDR) as a postcoital contraceptive. An oral dose of 2 mg dienogest was administered immediately after each coitus. The 58 women reported 872 intercourses during 302 cycles. Frequency of ingestion was on average 3 times per cycle. Pregnancy occurred in 14 women corresponding to a Pearl-index of 55.6. The observed pregnancy rate referring to all intercourses was 1.6 per cent. The incidence of expected pregnancies in relation to the coital exposures was 4.04 per cent. As a result the risk of pregnancy was reduced 2.5 times by dienogest. Menstrual disorders occurred in 18.9 per cent in regard of the total numbers of cycles. The results and an overview of literature suggest that neither dienogest nor other progestins are suitable as a sole contraceptive method when used as a postcoital agent. They are only indicated as a risk-reducing method after so-called "contraceptive emergencies".