In 31 patients with tranquilizer-and 13 patients with drug abuse the character and extent of changes in EEG during withdrawal period were studied and the influence of additional abuse of alcohol or barbiturates was investigated. The EEG showed pathological results in 22 patients (50%). Generalised spike activity was dominant, which was found more often in patients with tranquilizer abuse (35%) than in patients with drug abuse (15%). In patients with abuse of tranquilizers and additional alcoholism pathological EEGs were found more often (65%) than in the remaining patients (36%). Also in patients with additional abuse of barbiturates pathological EEGs (67%) were found more often. In patients with drug abuse with or without additional abuse of alcohol or barbiturates there was no difference between the number of normal and pathological EEGs. In patients with longer persistence of the tranquilizer abuse the number of pathological EEGs increased. Controls of the EEG revealed with increasing time interval an increasing number of normalised EEGs especially in patients without alcoholism of barbiturate abuse. Therefore the EEG revealed functional disturbances in the withdrawal period after abuse of tranquilizers or drugs which were more pronounced in patients with additional abuse or alcohol or barbiturates.