Glucocorticoid hormones, such as corticosterone and cortisol (CORT), are commonly used indicators of physiological stress in vertebrate animals. Despite being listed as an endangered species for over 50y and substantial research on decline of native habitat, response to environmental stressors, and physiology of other lizard species, no information is currently available on CORT physiology in blunt-nosed leopard lizards, Gambelia sila. This gap in knowledge limits our ability to assess relative stress levels among extant populations of G. sila or in response to captivity. We quantified corticosterone metabolites in opportunistically-collected fecal samples to assess baselines and natural variation in CORT throughout the active season. We also compared these CORT concentrations between a wild-reared population from the Panoche Hills Valley and a captive-reared population collected from the Panoche Hills Plateau and bred at the Fresno Chaffee Zoo. We validated and used a commercially-available corticosterone competitive enzyme immunoassay (EIA) to quantify the concentration of CORT metabolites in fecal samples. This provides an indication of the average amount of CORT circulating in the plasma during the period that the feces was produced. Our results provide an important baseline for future studies and repatriation efforts in this endangered lizard.