The bilateral spontaneous electrodermal activity (EDA) of four paid volunteer male students was recorded during three consecutive complete nights (after a habituation night). The results showed that: (a) there was a high proportion of electrodermal asymmetry (80%) during human sleep; (b) there were no significant differences in asymmetry between sleep stages; (c) electrodermal laterality during sleep seems to be under a random effects model; and (d) laterality appears to be an unreliable parameter. These results are discussed in terms of the activation theory.