We studied 225 healthy adult patients undergoing ENT, dental or orthopaedic surgery; they were allocated randomly to receive one of three different premedications, all given i.m. 1 h before operation. Group 1 received morphine 0.15 mg kg-1 and metoclopramide 10 mg; group 2 received morphine 0.15 mg kg-1 and glycopyrronium 5 micrograms kg-1; group 3 received morphine 0.15 mg kg-1 and hyoscine 5 micrograms kg-1. Patients who were premedicated with an anticholinergic had a significantly greater incidence and severity of postoperative shivering than those in the metoclopramide group. There was no difference in core temperature between patients who shivered and those who did not, either before or during the shivering episode. Shivering did not cause any clinically significant changes in heart rate, arterial pressure, ventilatory frequency or oxygen saturation. As this effect occurred with both glycopyrronium and hyoscine, it suggests that the mechanism by which postoperative shivering is influenced is peripheral to the central nervous system.