Renal function was evaluated in 12 children (aged 2.5-17.5 years) who received ifosfamide as part of their chemotherapy for different malignancies. A blood and urine analysis evaluating renal glomerular and tubular function and an isotopic determination of glomerular filtration were carried out four months or later after treatment had been stopped. Three patients had several biochemical abnormalities suggesting a significant degree of proximal renal dysfunction (increased urinary excretion of calcium, glucose, beta 2-microglobulin, amino acids (three patients) and decreased tubular reabsorption of phosphate (one patient)). The tubular dysfunction in these patients was associated with a diminished glomerular filtration. These patients could be characterized by their younger age at treatment and a higher dose of ifosfamide received if calculated per kg body weight.