A new method of synthesis of long-acting steroid derivatives is repo rted. Steroid hemisuccinates are reacted with N,N'carbonyl-diimidazole to form a very reactive intermediate, which is then esterified with a steroid alcohol to form a dimeric steroid. Dimeric, trimeric, and tetrameric estradiol derivatives synthesized by this method ahowed very long-lasting estrogenic effects in the Allen-Doisy test. Dimeric compounds were also formed by linking estradiol with cortexolone, with 17alpha ethinyl-5-androstene-3-beta-diol and with ethynodiol. These preparations also had a prolonged estrogenic effect. The dimer ethynodiol derivatives was shown to have a longer depot effect than progesterone or ethynodiaol diacetate. This technique may be useful in synthesizing depot steroids for contraceptive use.