The blood concentrations of propofol have been examined during anesthesia by continuous infusion of 12 mg/hg/hr. A bolus dose of 3 mg/kg body weight propofol was used to induce anesthesia. The mean concentrations at apparent steady state were in the range of 4.3 to 5.6 micrograms/ml during the infusion. The mean total body clearance, derived from the apparent steady state concentrations in the blood, was 0.0394 litres/kg/minute. The mean propofol blood concentration at awakening was found to be 2.3 micrograms/ml.