An enzymic method using alpha-glucosidases was adapted for measuring glycogen in very small samples (3 mg) of human endometrium. The method is useful as a clinical test of the physiologic function of human endometrium. The glycogen content of the endometrium of normal and infertile patients was measured during the menstrual cycle. The maximal content in both groups was observed between the 16th and 23rd days of the cycle, but the glycogen content of the infertile group was significantly lower (P less than 0.005). These results confirm the reports of others. Endometrial glycogen and urinary pregnanediol levels in 32 infertile patients were measured on day 7 after ovulation. The glycogen content of the endometrium of 21 of these patients, who showed normal excretion of urinary pregnanediol (greater than or equal to 2 mg/day), was significantly higher than that of the other 11 patients who showed low excretion of urinary pregnanediol (less than 2 mg/day) (P less than 0.005). This finding suggests that there is a high correlation between the function of the corpus luteum and endometrial glycogen deposition.