Long-term effects of 24-h sleep deprivation (SD) on sleep and sleep EEG were analyzed in male rats during 4 recovery days (Rec). An increase of total sleep time and non-rapid eye-movement (NREM) sleep was present during Rec 1-4, and of REM sleep in Rec 1 and in the dark periods of Rec 2 and 3. After the initial increase of slow-wave activity (SWA, mean EEG power density in the 0.75-4.0 Hz range) in NREM sleep, SWA declined below baseline until Rec 3. Sleep continuity was increased in Rec 1. The persistent effects of SD which are probably due to homeostatic and circadian facets of sleep regulation, must be taken into account in the design of SD studies.