Prior studies in adults have shown that metoclopramide (MCP), when given in high intravenous (IV) doses (2 mg/kg), is a highly effective antiemetic for chemotherapy-induced vomiting. It is well-tolerated in older adults, but younger adults have an increased disposition to acute extrapyramidal reactions (EPRs). Before studying the efficacy of MCP as an antiemetic in children, we first had to establish the safe dose range. We performed a dose-increase MCP toxicity study in children receiving highly emetic chemotherapy such as cisplatin (120 mg/m2) or cyclophosphamide (greater than 900 mg/m2), beginning with a dose of 0.2 mg/kg and increasing the dose in nine steps to 3 mg/kg. MCP was given every two hours for four doses beginning one-half hour before chemotherapy. To reduce the incidence of EPRs, we added concomitant diphenhydramine. In MCP doses less than 2 mg, toxicity was minimal. In doses greater than or equal to 2 mg, 4/27 (15%) had EPRs and 9/27 (33%) had akathisia. Children who received two consecutive days of MCP had a higher frequency of EPRs. Metoclopramide (2 mg/kg) had promising antiemetic efficacy in a preliminary nonrandomized trial. Chemotherapy-experienced children vomited fewer than five times in 9/21 (43%) trials, and new patients vomited fewer than five times in 7/10 (70%) trials. MCP will become more useful as an antiemetic in children if better measures to prevent EPRs can be developed. Chemotherapy-induced emesis has the same negative implications in children as it does in adults and optimum antiemetic regimens can only be discovered by conducting randomized clinical trials in children.