Electroencephalograms (EEC) of seven healthy male volunteers anesthetized with Forane were studied. Body temperature and Paco2were maintained at normal levels except that hypocapnia was transiently induced once or twice during each study. Increasing doses of Forane produced increasing periods of burst suppression, with complete electrical silence appearing at approximately 2½ per cent end-tidal Forane. At light levels of anesthesia, the frequency of electrical activity was 14 to 17 Hz at a maximum voltage of 120-180 microvolts. At subanesthetic concentrations (below 1.2 per cent) frequency increased and voltage decreased slightly. Hypocapnia did not alter these EEC findings. Audiostimulation could sometimes provoke an EEG response during an electrical silence. In no case was a convulsive EEC pattern (high-frequency, high-voltage spiging activity) seen. Forane-induced EEG changes can be distinguished from those seen with other anesthetics by the maintenance of high-frequency activity at any level where EEG activity is present. Depth of anesthesia can be monitored with the EEG.