Relatively little is known of the human ovum from just before the time of ovulation until after the time of implantation of the developing embryo in the uterus. Consequently the time of ovulation in the menstrual cycle in woman has been computed chiefly from the condition of the corpus luteum rather than from the finding of ova in the tubes. In an attempt to fill partly this gap in our knowledge of early human embryology, a cooperative investigation was planned with the following objectives: (1) the recovery of ova from the uterine tubes; (2) the correlation of their condition with the menstrual history and the stage of development of the early corpora lutea (recently ruptured follicles) from which these ova had been extruded, and (3) a continuance of quantitative analyses of the amount of ovarian hormone in tissues of the human ovary. Since the success of this work seemed to