We report herein the first observation of biopsy-proved rhabdomyolysis associated with macro-creatine kinase (macroCK) type 1 in a patient with diabetic nephrotic syndrome. A 42-year-old man with advanced chmonic complications of diabetes was admitted to the hospital with an episode of severe systemic edema caused by diabetic nephrotic syndrome. The patient was found to have elevated serum CK (2499IU/l, MM 89%), aldolase (25.1IU/l) and myoglobin (≥500ng/ml) levels. None of the known predisposing factors for rhabdomyolysis were present in this patient. Muscle biopsy showed rhabdomyolysis and muscle changes. The latter included both neurogenic and myogenic changes. Therapy for the nephrotic syndmome had not only decreased his body weight and edema but also serum enzyme levels. We speculate that subclinical muscle changes caused by diabetic neuromyopathy and general arteriosclerosis with excess interstitial edema caused rhabdomyolysis. Furthermore, macroCK was detected by gel electrophoresis as an atypical band between CK-MM and CK-MB and identified by immunofixation electrophoresis as containing CK isoenzymes MM and immunoglobulin A (λ).