A two-stage propofol infusion combined with fentanyl was used to maintain anaesthesia during coronary artery surgery in patients with good ventricular function. Whole blood propofol concentrations were measured at frequent intervals; plasma protein binding was measured before, during and after cardiopulmonary bypass. An initial infusion rate of 10 mg/kg/hour provided good protection from the pressor response to sternotomy. A predictable steady state concentration was achieved in the prebypass period with a maintenance infusion rate of 3 mg/kg/hour. The onset of bypass resulted in a small decrease in propofol concentration as a result of haemodilution. Induced hypothermia resulted in an increase in propofol concentration which returned rapidly to the prebypass steady state value during rewarming. The free propofol fraction increased during cardiopulmonary bypass. No patient had any recall of operative events or required inotropic support during weaning from bypass.