We determined baseline and capture-induced glucocorticoid concentrations during two different seasons in three species of wild free-living rodents: brown lemmings (Lemmus trimucronatus), golden-mantled ground squirrels (Spermophilus saturatus), and yellow-pine chipmunks (Tamias amoenus). Initial blood samples were all obtained within 3 min of capture, so that initial glucocorticoid levels reflect baseline titers of undisturbed animals. Animals were held for an additional 30 min, at which time a second blood sample was taken to measure stress-induced glucocorticoid titers. The primary glucocorticoid differed in each species. Lemmings secreted extremely large amounts of corticosterone, with concentrations as high as 8,000 ng/ml. These high concentrations were accompanied by high corticosterone binding globulin (CBG) capacities and resistance to negative feedback. Squirrels and chipmunks secreted a mixture of cortisol and corticosterone, in the 10-400 ng/ml range. Males of all three species, and female squirrels and chipmunks, showed significantly elevated glucocorticoid levels 30 min after capture. Both baseline and 30 min glucocorticoid levels differed seasonally in each species. Levels were higher during summer (with no snow cover) than in spring (with about 60% snow cover) in female lemmings, higher during breeding than before hibernation in squirrels, and higher post-reproductively than during breeding in chipmunks. Together, these data indicate that these free-living species have glucocorticoid responses to stress similar to laboratory species, but that the magnitude of the response appears dependant upon life-history features specific to each species.