A study was undertaken to evaluate the anti-emetic properties of halothane. One hundred and thirty female patients undergoing diagnostic dilatation and curettage, and cystoscopy, were given a standard premedication of atropine 0.65 mg and pethidine 50 mg. Of these, 42 patients were anaesthetized with thiopentone and anaesthesia was maintained using nitrous oxide and trichloroethylene; in 44 patients induction and maintenance were identical but each received 1 per cent halothane for the last 5 minutes of the procedure; and in 44 patients anaesthetic induction was similar but halothane and nitrous oxide were used for maintenance. As many variables as possible known to influence nausea and vomiting were excluded. The results show that a short exposure to halothane reduces the vomiting incidence following trichloroethylene by 50 per cent. Halothane alone was followed by a vomiting incidence of only one-eighth that of trichloroethylene.