In a randomised, double-blind study, a transdermal patch containing either hyoscine or placebo was applied post-auricularly in 190 adult patients under 65 year old, seven to twelve hours prior to their undergoing minor orthopaedic or plastic surgery under thiopentone/nitrous oxide/halothane general anaesthesia. In the first 24 hours after surgery 34% of patients vomited. The incidence of nausea (31% vs 54%; P less than 0.01) and the number of episodes of vomiting (66 vs 125; P less than 0.05) during the first 24 hours were significantly less with hyoscine than with placebo. The hyoscine group required fewer doses of antiemetic than the placebo group (12 vs 27; P less than 0.05). Side-effects were mild, the only difference between the two groups being the frequency of dry mouth immediately preoperatively. No differences were seen in the second 24 hours after surgery. We conclude that transdermal hyoscine is moderately effective in reducing the occurrence of postoperative nausea and vomiting following minor surgery.