ABSTRACTIn some recent reports, authors have found no evidence for habituation during sleep, and have concluded that habituation and sleep are incompatible. This finding was tested using skin potential, heart rate, and EEG responses to a 70 dB, 1 sec, 1000 Hz tone, in sleep stages 2, 4, and REM, with daytime controls. Interstimulus intervals used ranged from 10 to 30 sec.Autonomic responses analyzed separately for each series of stimuli showed significant habituation, except for heart rate responses in REM and in the daytime (drowsy) controls. EEG responses also demonstrated habituation. An interstimulus interval effect was found with EEG K‐complexes, habituation occurring more slowly or not at all with the longer, irregular interstimulus intervals.It is suggested that previous failure to detect habituation has been due to a technique of averaging responses over hourly periods and/or the use of long irregular interstimulus intervals. It is concluded that habituation is indeed possible in human sleep if stimulus intervals are not lon