The development of a new, long-lasting steroid implant contraceptive method based on the capacity of silastic to deliver progestogens at a slow and constant rate is described, beginning with the 1964 publication of early work on silastic. Following an early clinical finding of high proportions of ectopic pregnancy in cases of failure, the International Committee for Contraceptive Research (ICCR) was formed to compare results of trials in different countries and to promote development of a new form that would suppress ovulation. A large multicenter clinical study sponsored by the ICCR in 7 centers in Sweden, Denmark, Finland, Jamaica, the Dominican Republic, Brazil, and Chile included a double blind study of 2 different steroids administered in 6 silastic capsules, with the copper T 200 IUD used as a control. In this and other studies representing over 14 years of use, subcutaneous implants have been shown to be effective contraceptives with high acceptability. Levonorgestrel is apparently the most appropriate steroid because of its very low pregnancy rate of .4/100 woman years and its long period of effectiveness of 5 years. Secondary effects appear to be few, with menstrual disturbances especially in the 1st year the most troubling. The main factor limiting the diffusion of the method will probably be the skill required in inserting and removing the devices. Norplant is now the most effective reversible contraceptive available and is still undergoing improvement and modification.