Although dietary caloric restriction (CR) can retard aging in laboratory rats and mice, it is unclear whether CR can exert similar effects in long-lived species, such as primates. Therefore, we tested the effect of CR on plasma levels of dehydroepiandrosterone sulfate (DHEAS), a reliable endocrine marker of aging. The study included six young (approximately 10 years) and ten old (approximately 25 years) male rhesus macaques, approximately half of the animals in each age group having undergone >4 years of 30% CR. Hourly blood samples were collected remotely for 24 hours, through a vascular catheter, and assayed for DHEAS and cortisol. Both of these adrenal steroids showed a pronounced diurnal plasma pattern, with peaks occurring in late morning, but only DHEAS showed an aging-related decline. More importantly, there was no significant difference in plasma DHEAS concentrations between the CR animals and age-matched controls. These data fail to support the hypothesis that CR can attenuate the aging-related decline in plasma DHEAS concentrations, at least not when initiated after puberty.