Technique: An attempt was made to study a correlation of EEG, clinical anaesthetic depth and Fluothane concentration in blood by the Robson's method at Fluothane-Oxygen anaesthesia. Fourty-two adult human cases of both sexes, having no abnormal manifestations on EEG in awake state, were utilized for this analysis. Demerol, scopolamine and pentobarbital calcium were given in each case as a preoperative medication. Two % of F-O inhalation with semiclosed method was introduced for 25 minutes through a tracheal tube which has been inserted under consciousness by means of superior laryngeal nerve and translaryngeal blocking with 2 % xylocaine. 1) No EEG variation was observed in any case of the preoperative medication. 2) During F-O anaesthesia, however, a characteristic EEG patterns were found; increased amplitude and decreased frequency as the anaesthetic depth deepens. But slow waves were not detected until the depth becomes the 3rd plane of the Ⅲ stage or without hypercarbia. 3) The Fluothane concentration in blood appeares to be increased which the anaesthetic depth is deepened. 4) It seems to be concluded that both EEG manifestations and Fluothane concentration in blood maintain a parallel relation with the depth of F-O anesthesia. This is illustrated as follows
