Electroencephalographic (EEG) activity was monopolarly recorded during resting wakefulness in 10 volunteers under the following conditions: at night before going to sleep, at night before total sleep deprivation, in the morning after waking, in the morning after sleep deprivation and at night after having slept during the day. Absolute and relative power and inter- and intrahemispheric correlation were established. After diurnal and nocturnal sleep as compared to sleep deprivation, we obtained the following significant results: interhemispheric correlations were higher; intrahemispheric correlations were lower; absolute power of alpha 2, beta 1 and beta 2 was lower; and relative power of alpha 2 and beta 2 was lower. EEG changes as a consequence of sleep or lack of sleep are dependent on prior sleep and/or wakefulness and not on circadian phase. EEG activity during wakefulness is a sensitive parameter and a useful tool to assess the consequences of sleep on brain functional organization.