Continuous telemetric EEG recordings served to determine the vigilance states of the rat during 2 control days, 80 h of food deprivation and 64 h following restitution of food. The recordings were supplemented by measurements of food intake, water intake and motor activity. The following 3 sleep parameters were not significantly changed by food deprivation: the daily amount of the vigilance states, the light-dark distribution of sleep and waking, and the 10 min paradoxical sleep (PS) cycle. During food deprivation, PS was depressed in the dark phase of the diurnal cycle and increased in the light phase. The sleep parameter that was most affected by food deprivation was the duration of sleep episodes. Episodes of slow-wave sleep (SWS) and PS were shortened only in the dark phase of the deprivation days, whereas total sleep episodes were progressively decreased in both diurnal phases. After restitution of food, the episodes of SWS and total sleep were immediately lengthened and tended to exceed the control level. The duration of feeding episodes and meal size were significantly increased in comparison to pre-deprivation values, whereas feeding frequency was decreased. Long episodes of continuous motor activity occurred during the dark phase of the refeeding period, while a fragmented activity pattern was typical for the deprivation nights. It is proposed that the adjustment of the length of behavioral episodes may constitute an important adaptive mechanism for the rat.