The calorie and protein requirements were studied in 6 pediatric patients with acute nonlymphocytic leukemia treated in a laminar air flow unit. Calorie and protein requirements were estimated from anthropometric data. Mean total caloric requirement for weight maintenance was 136% of estimated basal metabolic rate, which is much lower than the RDA for healthy children. The mean protein requirement was 108% RDA. Provision of intravenous nutrients depressed oral intake. Infection had a deleterious effect on visceral protein status as determined by serum albumin.