Dehydroepiandrosterone (DHEA) and its sulfate, DHEAS, are the most abundant steroid hormones in primates, providing a large reservoir of precursors for the production of androgens. DHEAS levels decline with age in adult humans and nonhuman primates, prompting its consideration as a biomarker of senescence. Moreover, recent studies in humans have suggested that DHEAS can increase in stressful situations. However, the mechanisms responsible for this age-related decrease and its relationship to stress in nonhuman primates remain elusive. We developed and tested a non-invasive method to evaluate DHEAS concentrations in Japanese macaques (Macaca fuscata) using feces. The subjects were 39 female Japanese monkeys from 2 weeks to 31 years old, kept in captivity at the Primate Research Institute, Kyoto University (27 monkeys in outdoor social groups and 12 monkeys living in single indoor cages). We collected approximately 3 fecal samples per individual from all females between October and December of 2011. These samples were analysed for DHEAS by enzyme-immunoassay. We found that age is negatively associated to DHEAS levels, but this age-related decline was more evident in females housed individually indoors than in females housed outdoors in social groups. We also found extremely high concentrations in neonates. Since DHEAS is believed to be involved in aging, memory, cognition, and in the immune system, we suggest that DHEAS might play an important role in infant development. The environment had a significant impact in DHEAS, with higher levels in females housed indoors in single cages, than in those living outdoors in social groups. This finding supports the hypothesis that DHEAS levels respond to stress, and decrease with increasing age in Japanese macaques. Our study provides insights about the physiology of this adrenal hormone in female Macaca fuscata and we are currently examining these hormones in free-ranging populations.