Premedication with diazepam 0.25 mg kg-1 by mouth was compared with placebo in a double-blind trial in patients undergoing day-case surgery under general anaesthesia. Diazepam decreased significantly preoperative discomfort and apprehension. The patients were discharged on time regardless of the type of premedication, and complaints at the time of discharge and on the following day could be related only to the length of anaesthesia and not to the type of premedication. Premedication given early in the morning remained effective for up to 6 h.