text: A 10-year-old boy with osteosarcoma and normal renal function manifested laboratory evidence of impending renal toxicity and extreme elevation of aspartate aminotrasferase and alanine aminotransferase within 2 hours after the completion of a 4-hour infusion of high-dose methotrexate (MTX) (12 g/m2), and went on to develop acute renal failure with life-threatening hyperkalemia 29 hours later.