Subdermal implants are contraceptive systems that release low, stable amounts of synthetic progestins from Silastic or other materials for periods of months to several years. Unlike other hormonal delivery systems, they do not cause unnecessary peaks in progestin levels and do not use estrogens, and thus their health risks are minimal. Norplant has been studied more extensively than any other subdermal contraceptive implant. More than 60,000 women have participated in clinical trials, which demonstrated that this approach is one of the most effective reversible contraceptive methods available (1% pregnancy rate in 5-year users). The implant also reduces the incidence of ectopic pregnancy to a level much below noncontraceptive users and about equivalent to TCu380A intrauterine device users. Exposure to the sustained, low dose of levonorgestrel delivered by Norplant has shown only minor metabolic changes. Side effects are minor but often bothersome, causing some discontinuation of the method. First-year continuation rates range from 76% to 90%. Fertility return after discontinuation is prompt. Difficulty in removal of the implant capsules by the less experienced practitioner has motivated researchers to develop systems that are easier to use, less obvious under the skin, and biodegradable. The Norplant 2 system is faster, easier, and less painful to insert and remove. Implants under investigation release desogestrel and other progestins; Capronor and subdermal norethindrone pellets are biodegradable systems.