Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, estradiol, and progesterone concentrations were measured in 58 ovulating women in different age groups (20 to 29, 34 to 39, 40 to 44, and 45 to 50 years) at five- to seven-day intervals through a single menstrual cycle and in 18 postmenopausal women sampled weekly five to six times. The over-all hormone patterns were similar in four premenopausal groups. However, mean serum FSH levels increased with age and significantly higher concentrations were found in the 40 to 50 years group than in the 20 to 29 year group. Serum LH levels did not show a similar rise with age, although follicular LH levels in the oldest group were higher than in the 20 to 29 year group. Prolactin and estradiol concentrations did not change with age prior to the menopause, but luteal progesterone levels were lower in the three older premenopausal groups than in the 20 to 29 year group. Postmenopausal women showed elevated FSH and LH, decreased prolactin, and negligible estradiol and progesterone levels. There was an over-all significant linear correlation between prolactin and estradiol concentrations. It appears that the menopause is preceded by several years of rising gonadotropin, predominantly FSH, levels. During this period, ovarian estrogen production appears to be maintained and ovulation continues, but luteal progesterone levels decline. It is likely that these premenopausal alterations in pituitary-ovarian relationships reflect depletion of ovarian follicles.