Between 1980 and 1986, 44 children with acute lymphoblastic leukemia (ALL) or Stage IV neuroblastoma (NB) underwent allogeneic or autologous bone marrow transplantation (BMT). Twenty-nine of these patients were alive and in remission 3 months post BMT and were evaluable for this analysis of whom eleven have developed renal dysfunction. Six of 17 (35%) evaluable ALL patients developed renal dysfunction (3.5 to 6 months post BMT). This group was transplanted for CALLA positive ALL and received an autologous transplant. Preparation included tenopiside (VM 26) cytosine arabinoside, and cyclophosphamide followed by total body irradiation (TBI). One patient received 850 cGy in a single fraction, while all other patients received fractionated TBI (1200-1400 cGy in 6-8 fractions over 3-4 days). Five of 7 (71%) evaluable patients who received a BMT for NB have developed late renal problems (4-7 months after BMT). The preparation for NB patients included VM 26, cis-platinum, melphalan, cyclophosphamide, and fractionated TBI (1200-1296 cGy). All seven NB patients had received cis-platinum as induction treatment prior to transplantation. All patients presented with anemia, hematuria, and elevations of BUN and creatinine. Two patients underwent renal biopsies which were consistent with radiation nephropathy or hemolytic uremic syndrome. In conclusion, a high incidence of renal dysfunction has occurred 3 to 7 months after BMT for children with NB and ALL. The clinical and laboratory features are consistent with either acute radiation nephropathy or hemolytic-uremic syndrome. These patients were prepared for BMT with multiple chemotherapeutic agents as well as TBI. The relatively young age of these patients and conditioning with intensive multi-agent chemotherapy may decrease the tolerance of the kidney to radiation injury.