Seven children with previously treated brain tumors were enrolled in a phase I trial of 5-day continuous-infusion procarbazine at 360, 480, and 638 mg/m2/day. Vitamin B6 levels were monitored. Myelosuppression was moderate though occasionally delayed, and nausea and vomiting were mild. At the highest dose level, a patient experienced severe psychosis that persisted for several weeks. From that dose-limiting toxicity and the degree of myelosuppression, the recommended dose for phase II trials in children is the same as for adults, 450 mg/m2/day.