One hundred and twelve women undergoing elective orthopaedic surgery under enflurane anaesthesia were given, in a double-blind random fashion, 2.5 mg of droperidol i.m. before anaesthesia, or 1.25 mg of droperidol or a saline placebo i.v. at the end of anaesthesia in an attempt to prevent post-operative vomiting. The administration of droperidol 1.25 mg (for those receiving initially 1.25 mg of droperidol) or saline (for those receiving initially 2.5 mg of droperidol or saline) was repeated i.m. during the 24 post-operative hours in a blind manner if the patient complained of nausea, retched or vomited. Significantly fewer patients (P less than 0.05) given i.m. or i.v. droperidol had emetic symptoms than patients given saline. Furthermore, 51% of the patients given saline needed additional doses of saline, whereas only 27% of the patients given i.m. and 36% of the patients given i.v. droperidol required a second dose (P less than 0.05 between groups). More of the patients given saline (23%) than those given droperidol (8% to 9%), as a blind drug (P less than 0.05), needed to be given additional droperidol as a known anti-emetic because of the failure of the blind drug to prevent or treat symptoms. It is concluded that droperidol given either as a single dose of 2.5 mg i.m. or in repeated doses of 1.25 mg i.v. is effective in the prevention and treatment of post-operative nausea and vomiting after enflurane anaesthesia.