Emesis is a major problem for children receiving cancer chemotherapy. Three open non-comparative studies have been conducted to assess the safety and efficacy of ondansetron in children receiving a variety of chemotherapy regimens. Patients received various dosages of ondansetron, intravenously or intravenously plus orally, 8-hourly, during chemotherapy, followed by oral treatment 8-hourly for 3-5 days following chemotherapy. Complete control of emesis was achieved in 42-87% of children, and complete plus major control (0-2 emetic episodes) was achieved in 65-98% of children during their chemotherapy treatment, which varied from 1-8 days, and in 54-92% of children over the total study period. Ondansetron was effective in children receiving a wide variety of chemotherapy regimens. However, more intensive chemotherapeutic regimens and platinum drugs are associated with lower response rates. Ondansetron was well tolerated and none of the patients experienced extrapyramidal symptoms.