Despite its many disadvantages ketamine may offer a partial answer to the pollution of the operating room by gases and vapours. It is a relatively long-acting drug with good analgesic action and does not require supplementation with nitrous oxide. This study was carried out to investigate the efficiency of the ketamine I.V. drip technique in patients undergoing operations not requiring tracheal intubation, muscle relaxation and controlled ventilation. The only contraindications to the use of its technique were hypertension, a history of a cerebrovascular accident or undetermined history of psychiatric upset. Twenty patients, ranging in age from 20 to 60 years, were premedicated with atropine and secobarbital, diazepam or hydroxyzine. Anesthesia was induced with 0.15mg/kg droperidol in Thalamonsl and was maintained with 0. 1% ketamine in 5% dextrose or balanced salt solution. The average dosage of ketamine was 1.175 mg/kg/hr for induction and 2. 33 mg/kg/hr for maintenance during operations with duration from 20 minutes to 5 hours and 35 minutes. No supplementary general anesthesia was given, but when the depth of anesthesia was :not adequate, the rate of the ketamine infusion was increased. After the induction with Thalamonal the respiration rates were decreased temporarily, but the tidal volume and arterial gas study were clinically within normal limits. The incidences of complications of anesthesia, namely increased B.P. (20mmHg above preoperative value), involuntary movements, dreams and hallucinations were 60, 40, 10 and 5% respectively. The verbal response time from the end of operation was within 30 minutes in 75% cases. It may be concluded that Thalsmonal and ketamine I.V. drip anesthesia without intubation can be used relatively satisfactorily in operations in which muscle relaxation, endotracheal intubation and controlled respiration are not needed.