Sleep, daily torpor and hibernation are considered to be homologous processes. However, during periodic arousals from hibernation, ground squirrels spent most of the euthermic period in non-REM sleep. Therefore, it has been proposed that animals arouse regularly from hibernation to recover from a sleep deprivation (SD) incurred during hibernation. We demonstrate in the Djungarian hamster that EEG slow-wave activity (EEG power density in the 0.75-4-Hz range), which is increased after SD, is enhanced in a similar way after an episode of daily torpor. The results support the hypothesis that daily torpor is incompatible with the restorative function of sleep.