AMENORRHEA and sterility are frequent accompaniments of morphine addiction in the human female (Menninger-Lerchenthal, 1934; Pescor, 1938). The mechanisms by which these effects are induced, however, are not clearly understood. In experimental animals results are contradictory. Myers and Flynn (1928, 1931) failed to observe any disturbance of estrous cycles, ovulation or fertility despite 132 days of chronic morphine treatment in rats, and their results were confirmed by Forster (1928). In contrast, treatment of mice daily for a two-month period with morphine has been reported to suppress estrus and induce atrophy of the ovary and uterus (Ko, 1934). Similar observations were noted in the rabbit (Bun, 1937). The finding by Everett and Sawyer (1950) that “spontaneous” ovulation in the rat involves a neurogenic timing factor with a 24-hour rhythmicity offers a new approach to the study of the control of ovulation.