Abstract:EEGs were recorded for Fpl, C3 and O1 once a week for 4 weeks after the withdrawal of medazepam, a benzodiazepine with a long half‐life, from 7 normal males. Quantified analyses of them showed 2 types of change: A maximum change during the administration of medazepam that later tapered off. It consisted mainly of an increase in fast wave, and was uniform across areas though most significant in C3. A rebound phenomenon that reversed the change produced by the drug, the decrease in fast wave being significant in C3 during week 2. These results suggest that fast wave is the most sensitive EEG element and these 2 types of change must be investigated hereafter in terms of significant changes after the discontinuation of medazepa