Spontaneous electrodermal activity (EDA) (galvanic skin response [GSR] and skin potential response [SPR]) was recorded during daytime sleep and nighttime sleep. During all sleep, spontaneous EDA occurred most frequently during stages 3 and 4 (slow wave sleep) and least frequently during stage 1 (rapid eye movement [REM] and non-REM). This pattern was consistent over 3 nights of sleep. There was no relation between waking and sleeping spontaneous EDA. The spontaneous EDA during slow wave sleep significantly exceeded that during waking. During sleep, spontaneous SPRs often occurred without spontaneous GSRs.