The clinical evaluation of drugs used in fertility regulation is initially assessed in Phase I, II and III trials. The design of each phase and the investigative staff must be adequate. In Phase I, normal, healthy human volunteers meeting specific guidelines are usually studied. Numbers vary between 20 and 80 and the purpose is to determine the acute toxicity of the compound. In Phase II, efficacy and safety are examined in a clinical target population, and emphasis may be placed on pharmacological and mechanistic studies. Usually between 50 and 200 patients are involved. In Phase III, large-scale clinical studies for local registration and the introduction of drugs to various countries are included. This paper describes the evaluation of various drugs used in contraception, including NORPLANT implants, and considers the efficiency, safety and acceptability of such drugs. Phase IV studies are usually needed to reveal chronic toxicities or rare events.