AbstractFifteen female rhesus monkeys (Macaca mulatto), ranging in age from 8 to 34 years, were studied for one year to characterize the endocrine and menstrual changes associated with menopause in this species. Five monkeys were premenopausal; these younger monkeys, ages 8–11 years, menstruated and showed cyclic ovarian activity during the 12–month study period, as evidenced by menses and periodic elevations of serum estradiol (E2) and luteinizing hormone (LH) concentrations. Four females, ages 24–26 years, were in transition to menopause. Two of these perimenopausal females menstruated and secreted E2and LH in a periodic fashion; the other two females showed elevated LH concentrations, consistently low E2levels, and no evidence of menstruation. Six females, ages 27–34 years, were clearly postmenopausal; LH concentrations were high, whereas E2concentrations were uniformly low. There was a significant inverse correlation between basal E2concentrations and age, and a significant positive correlation between age and LH concentrations across all 15 animals. Hormonal changes indicative of ovulation, when they occurred, were generally restricted to the winter and early spring months. Histological analysis of ovaries from four postmenopausal females revealed little or no evidence of active folliculogenesis. These data indicate that menopause in female rhesus monkeys does not occur until the second half of thethird decade of life. © 1995 Wiley