Thirty-three patients undergoing elective aortocoronary bypass were allocated randomly to receive morphine 0.1 mg kg-1 i.m. and either lorazepam 50 micrograms kg-1 by mouth or hyoscine 6 micrograms kg-1 i.m. before rapid sequence induction of anaesthesia with sufentanil 5 micrograms kg-1 i.v.and suxamethonium 1 mg kg-1 i.v. Following induction and tracheal intubation, patients premedicated with hyoscine had a significantly higher mean heart rate, mean arterial pressure, cardiac index and left ventricular stroke-work index than patients premedicated with lorazepam. The incidence of new myocardial ischaemia was low in both groups.