Fecal hormone analysis is a useful tool for frequent, non-invasive sampling of free-living animals. Estrogens fluctuate throughout life among reproductive states in female animals, and intensive repetitive sampling can permit accurate assessment of female reproductive condition. This type of repetitive sampling is difficult in large carnivores, including the spotted hyena (Crocuta crocuta). Patterns of estrogen secretion in captive and free-living hyenas are virtually unknown. Here we present validation of an enzyme-immunoassay to measure fecal estrogen (fE) concentrations in wild and captive spotted hyenas. Results from high-performance liquid chromatography indicate that an antibody specific for estradiol exhibits high immunoreactivity with our extracted samples. Fecal extract displacement curves paralleled our estradiol standard curve within the range of 20 -80% antibody binding. Additionally, animals treated with luteinizing hormone-releasing hormone showed a measurable rise in fE concentrations. Finally, once we controlled for effects of time of day of sample collection from wild hyenas, patterns in fE concentrations resembled those in plasma estradiol, including higher levels of fE in mature than immature females, and higher levels of fE during late than early pregnancy. Together, these results suggest that fE concentrations reflect circulating estrogens in spotted hyenas.