Ondansetron was compared with conventional-dose metoclopramide in a randomised trial for emesis control in 56 patients with lymphoma and leukaemia receiving commonly used chemotherapeutic regimens that are moderately emetogenic. Emetogenic chemotherapeutic agents were administered on day 1 to lymphoma patients and on days 1 to 5 to leukaemia patients. Ondansetron was superior to metoclopramide in the complete control of acute emesis (75vs43%, p = 0.03). Control of delayed emesis in lymphoma patients was marginally better with ondansetron on days 2 (89vs64%, p = 0.140) and 3 (94vs68%, p = 0.054). Continuous control of emesis for leukaemia patients on daily chemotherapy was better with ondansetron on days 3 (80vs17%, p = 0.035) and 4 (90vs33%, p = 0.036). Furthermore, significantly more patients on ondansetron enjoyed normal food intake on day 1 (71vs14%, p = 0.000). Both antiemetic regimens were well tolerated. No extrapyramidal reactions were observed.