ABSTRACTThe number of nocturnal galvanic skin responses‐(GSRs) varied widely between the electroencephalograph (EEG) stages of sleep as well as from night to night and from person to person. As others have found, non‐specific GSRs occurred much more frequently during stage IV than other EEG stages, and were rare in stage REM. However, night‐to‐night variation and individual differences were related to the presleep state of the person. In general, electrodermal activity increased in all EEG stages as daytime stress increased, being especially great on nights preceding important school examinations.The nocturnal EEG profile was also related to the presleep state, the percentage of stage IV decreasing as daytime stress increased. The percentage of stage REM showed no systematic relation to stress.The occurrence of GSR “storms” during slow‐wave sleep is consistent with the notion of release of cortical or other inhibitory influences during this state, but another mechanism is needed to explain the fact that presleep stress increases the frequency of GSRs in all stages of sleep, while simultaneously decreasing the percentage of sl