The anaesthetic properties of alfentanil were evaluated in 15 patients undergoing coronary artery bypass grafting operations. Alfentanil was infused at a rate of 3.0 mg min−1 until the patients (breathing pure oxygen) became unconscious. Additional alfentanil 2.5–5.0 mg i.v. was given if systolic arterial pressure increased by 15% or more from control values. Alfentanil produced unconsciousness in 75±18s, but muscle rigidity occurred in 27% of patients. Cardiovascular dynamics were minimally altered during the induction of anaesthesia and throughout most of the operation, although 60% of patients became hypertensive during stemotomy and 73% during sternal spread. Recovery from anaesthesia was rapid with patients regaining consciousness after 1.4±0.6 h and fulfilling our criteria for extubation of the trachea 4.1±1.2 h after operation. No patient was aware of laryngoscopy, endotracheal intubation or any aspect of the operation.