“…The compounds include a group synthesized by the Merrell Company (MER-25 and clomi¬ phene, MRL-41) and a group produced by the Upjohn Company (U-l 1555A, U-10520A and U-11100A). Most of the investigations have involved the antifertility effects of injected or oral doses during the first few days of pregnancy in the rat (Barnes & Meyer, 1962;Davidson, Schuckner & Wada, 1965;Duncan, Stucki, Lyster & Lednicer, 1962;Nelson, Davidson & Wada, 1963;Segal & Nelson, 1961). During this period the zygotes are undergoing cleavage and blastocyst formation, while being transported through the oviduct to the uterus, in preparation for implantation.…”