To evaluate the nutritional consequences of acute lymphoblastic leukemia and its treatment, 15 children with leukemia were studied. Anthropometric data, fat-free mass by impedance, energy intake, and resting energy expenditure (REE) were determined at diagnosis and on days 22, 36, and 71 of the treatment. Interleukin (IL)-1 beta, IL-6, interferon-gamma, and tumor necrosis factor were also measured. Fifteen healthy control subjects were matched for age and sex. Body weight and height and body composition were comparable at all times of the study, although three children were underweight at diagnosis (weight-for-height < 85% of French standards). Although two different methods were used for dietary recall in the two groups, energy intake expressed as a percentage of normal recommended values for age and sex was lower in patients than in control subjects (104 +/- 19%) on day 1 (47 +/- 32.1%) and day 22 (58 +/- 24%), but was comparable on day 36 (85 +/- 71%) and day 71 (85 +/- 48%). This low energy intake involved both carbohydrates and fats. Energy and carbohydrate intakes improved significantly during the study in patients. The nonprotein respiratory quotient (RQ) in patients was significantly lower than in control subjects (0.84 +/- 0.04) on day 1 (0.79 +/- 0.02) but was comparable on day 71. The REE of the patients on day 1 (5057.8 +/- 1588.4 kJ/24 h) and day 71 (4844.7 +/- 116.1 kJ/24 h) and of the control subjects (4313.8 +/- 823.5 kJ/24 h) was not significantly different. Cytokines remained undetectable on days 1, 36, and 71. The results showed that at the time of diagnosis and during this period of chemotherapy there was no evidence of raised REE. The poor intakes during the first month of chemotherapy were recent as shown by the parents' questionnaire responses and the absence of consequences in body composition. The transient decrease in RQ seemed to be an adaptative mechanism to the poor carbohydrate intake. No indication of undernutrition in the patients as a group was evident during the first 71 d of treatment although further long-term nutritional assessment is needed.