A 73-year-old woman with chronic renal failure developed generalized muscular weakness and pain 6 days after the start of allopurinol treatment(200 mg/day). Routine laboratory tests revealed elevated levels of serum creatine kinase, and the patient was clinically diagnosed as rhabdomyolysis, due probably to severe myositis. A high level of serum oxipurinol, the chief active metabolite of allopurinol, was also revealed. The muscular weakness was relieved in seven weeks with intermittent hemodiafiltration.