The aim of this study was to analyze the electroencephalographic alterations produced by minimum doses of midazolam and look for a theoretic base for these changes in the benzodiazepinic receptor. To do so, the possible abnormal responses provoked by midazolam on the EEG of patients with ischemic cerebral infarctions were studied. Sub-hypnotic infusions of midazolam (0.15 mg kg/min) were administered prior to anesthetic induction in three groups of patients: control group, patients with tumoral cerebral pathology group, and ischemic cerebral infarctions group. In addition to the known modifications obtained in the patients of the control group, those presenting bioelectric activity alterations due to tumoral pathology did not show modifications. In the group of patients with ischemic infarctions, the intravenous perfusion of midazolam induced moderate increase in the localized theta and delta frequency and a lower representation of the beta rhythm which was also of lower amplitude. Midazolam is capable of making slow rhythms on the EEG, following it administration at low doses, in ischemic zones of the brain.