Fecal corticosteroid levels were monitored in free-living populations of deer mice (Peromyscus maniculatus) and southern red-backed voles (Clethrionomys gapperi) in North-Central Idaho. Sex, reproductive condition and age had no significant effect on fecal corticosteroid level in either species, but fecal corticosteroid levels were significantly higher in deer mice than red-backed voles regardless of sex or age. These data are consistent with the plasma corticosterone level profile exhibited by wild-caught individuals of both species maintained in captivity. In addition, for deer mice estimated population size was significantly correlated with fecal corticosteroid levels. Overall, these data clearly indicate the utility of fecal corticosteroid measures in assessing the adrenal status of wild populations of rodents.