BACKGROUND Breast surgery is associated with a relatively high incidence of postoperative nausea and vomiting (PONV). This study was undertaken to evaluate the efficacy of granisetron, droperidol and metoclopramide for preventing PONV after breast surgery. METHODS In a randomized, double-blind, placebo-controlled trial, 120 female patients received granisetron 40 micrograms.kg-1, droperidol 1.25 mg, metoclopramide 10 mg or placebo (saline) (n = 30 for each) intravenously immediately before the induction of anaesthesia. A standard general anaesthetic technique was employed throughout. Postoperatively, during the first 24 h after anaesthesia, the incidence of PONV and adverse events was recorded. RESULTS The incidence of PONV was 17% with granisetron, 37% with droperidol, 43% with metoclopramide and 50% with placebo (P < 0.05; overall Fisher's exact probability test). The incidence of adverse events was not different among the groups. CONCLUSIONS Granisetron is highly effective for reducing the incidence of PONV in female patients undergoing breast surgery. Droperidol and metoclopramide are ineffective in this population.