To determine the contribution of metoclopramide to the efficacy of ondansetron in control of cisplatin-induced emesis, ondansetron was compared with ondansetron plus metoclopramide for antiemetic efficacy in a randomized double-blind trial. Enrolled 66 patients were treated with cisplatin(60mg/m2) in combination with etoposide, flourouracil, or vinblastine, and randomized to receive either ondansetron alone or ondansetron plus metoclopramide. Sixty patients were evaluable. Complete or major control of acute emesis was achieved in 96.6% (29/30) of patients given ondansetron plus metoclopramide and in 80% (24/30) receiving ondansetron alone, with no statistical significance (P = 0.07). However, delayed emesis (days 2-6) was better controlled by combination therapy than by ondansetron alone with 22 of 30 (73.4%) and 11 of 30 (36.7%), respectively (P = 0.03). No major drug-related side effects were observed. These results suggest that ondansetron plus metoclopramide is superior to ondansetron alone in the control of cisplatin induced delayed emesis without significant side effects.