Long-acting forms of contraception that take advantage of the tissue compatibility of silicone rubber, a polymer of dimethylsiloxane, have been developed. The most advanced type of subdermal contraceptive capsule contains about 36 to 40 mg of levonorgestrel and is 30 mm in length and 2.4 mm in diameter (Norplant). The set of six implants is placed under the skin of the upper arm with a 10-gauge trocar with the use of a local anesthetic. The basis for the antifertility effect of these implants is continuous, low-dose progestogen therapy without the use of estrogen. The capsules release a total of approximately 39 micrograms of levonorgestrel each day. The blood progestogen level achieved through this microabsorption delivery system is 0.25 to 0.3 ng/ml. There is a sufficient supply of steroid in the capsules to maintain this blood progestogen level for 5 to 6 years. Since the capsules can be removed at any time, this contraceptive method is voluntarily reversible. The effectiveness of these subdermal implants has been evaluated in long-term studies that have progressed for well over 5 years. Therefore one clinic visit eliminates nearly 2000 days of concern over having to remember to take a pill on schedule. There has been sufficient experience to assure that fertility recurs promptly after removal of the subdermal implants.