To investigate the relationship between thermoregulation and sleep regulation, rats were sleep-deprived for 3 hours at two different ambient temperatures. Sleep deprivations (SD) were performed at 23 degrees C (SD-23) and at 32 degrees C (SD-32) in the beginning of the 12-h light period in animals chronically implanted with ECoG and EMG electrodes, and with epidural and hypothalamic thermistors. SD-32 enhanced cerebral temperature more than SD-23 at both brain sites. The SD-induced hyperthermia was followed by a fall of brain temperature below baseline. During recovery from either SD procedure, waking was reduced and sleep continuity increased. REM sleep was increased after SD-32. EEG slow-wave activity (spectral power density in the 0.75-4.0 Hz band) exceeded the baseline level in the first 3-h interval of recovery; however, the effects of SD-23 and SD-32 did not differ. In the same time interval, power density in the 1.25-1.5 Hz bin as well as in some bins in the theta and alpha band was higher after SD-32 than after SD-23. The increase in hypothalamic temperature during SD did not correlate with the increase in SWA during recovery. It is concluded that even a brief SD has major repercussions on recovery sleep whereas the extent of cerebral hyperthermia during SD is only a minor factor.