The effects of halothane, diethyl ether, N_2O, and enflurane on the cerebral metabolic rate for oxygen (CMRo_2) and EEG were studied in forty-four dogs. With halothane, the CMRo_2 progressively decreased, being accompanied by irregular slow-wave activity. With N_2O the CMRo_2 significantly increased, N_2O was completely blocked by pretreatment of thiamylal. With enflurane produced seizure-activity of the EEG. These results indicated that the decreased or unchanged CMRo_2 may be observed during anesthesia. There was no universal relationship between CMRo_2 and EEG.