The role of the uterus in the maintenance and regression of the corpus luteum was investigated in 7 patients who underwent hysterectomy for leiomyomata. Except in one patient, hysterectomy was performed in the postovulatory phase of the cycle. The patients were evaluated by preoperative and postoperative urinary pregnanediol determination, visual inspection of the ovaries and histologic examination of the endometrium. The data indicate that hysterectomy did not prolong the life span of the corpus luteum in the operative cycle, and cyclic ovarian function occurred after the operation. It appears that, in contrast to the situation in lower species, a uterine luteolytic factor is not involved in regulating the life span of the human corpus luteum. A self-regulatory mechanism in the corpus luteum itself is probably involved in the regression of luteal function in the human.