The adrenal steroids, dehydroepiandrosterone (DHEA) and its sulfate (DHEAS), have attracted attention for their possible antiaging effects. DHEAS levels in humans decline markedly with age, suggesting the potential importance of this parameter as a biomarker of aging. Here we report that, as seen in humans, male and female rhesus monkeys exhibit a steady, age-related decline in serum DHEAS. This decline meets several criteria for a biomarker of aging, including cross-sectional and longitudinal linear decreases with age and significant stability of individual differences over time. In addition, the proportional age-related loss of DHEAS in rhesus monkeys is over twice the rate of decline observed in humans. Most important is the finding that, in rhesus monkeys, calorie restriction, which extends life span and retards aging in laboratory rodents, slows the postmaturational decline in serum DHEAS levels. This represents the first evidence that this nutritional intervention has the potential to alter aspects of postmaturational aging in a long-lived species.