This study was undertaken to determine the minimum effective dose of granisetron, a selective 5-hydroxy-tryptamine type 3 receptor antagonist, for the prevention of post-operative nausea and vomiting (PONV) in female patients undergoing elective laparoscopic cholecystectomy. In randomized, placebo-controlled, double-blind study, 120 women were assigned to receive either placebo (saline) or granisetron at three different doses (20 μg kg−1, 40 μg kg−1 or 80 μg kg−1) intravenously immediately before the induction of anaesthesia. All patients received standardized aesthesia consisting of isoflurane and nitrous oxide in oxygen. The incidence of PONV during the first 24 hours after anaesthesia was 43, 40, 13 and 13% after administration of placebo and granisetron 20 μg kg−1, 40 μg kg−1 and 80 μg kg−1, respectively (P<0.05, overall Fisher's exact probability test). Adverse effects post-operatively were not different among the groups. In conclusion, granisetron 40 μg kg−1 is the minimum effective dose in the prevention of PONV after laparoscopic cholecystectomy.