Renal function tests (cystatin C, serum and urine creatinine, creatinine clearance, serum and urine beta(2)-microglobulin, microalbuminuria, osmolality) were performed in 21 children at the diagnosis and during the treatment for acute lymphoblastic leukemia (ALL) (group I) and in 37 children (group II) treated for ALL 3.9+/-3.7 years before the study. The results were compared to 20 healthy children. Mean values of renal tests were in normal range at all points of analysis in groups I and II compared to the control group. Transitory higher cystatin C values (but in normal range) were observed after methotrexate administration and after the end of treatment. Deteriorated renal function was observed in one child during the treatment (after each protocol) and in five children treated previously for ALL. In conclusion, combined treatment for ALL is not associated with severe or long-term impairment of renal function.