Plasma corticosterone (CORT) levels were measured after short periods of sleep deprivation in rats at postnatal days 12, 16, 20, and 24. There was an age-dependent increase in basal CORT levels and sleep deprivation significantly elevated CORT at all ages compared to non-sleep deprived controls. The levels of CORT after sleep deprivation in P16, P20 and P24 animals were similar, resulting in an age-dependent decrease of the magnitude of the response. Sleep deprived P12 animals had lower levels of CORT. However, the observed response to sleep deprivation suggests that sleep loss is a significant stressor at this age. These observations suggest that younger animals are more sensitive to the effects of mild sleep deprivation than older ones.