A 60-year-old man with advanced chronic complications of diabetes was found to have an elevated serum creatine kinase (6867 IU/l, MM 100%) level during an episode of systemic edema caused by diabetic nephrotic syndrome. There were no myogenic changes causing enzymes to leak from the muscle in electromyogram and muscle biopsy, though slight muscle atrophy and neurogenic changes were found. The patient had neither hypothyroidism nor diabetic ketoacidosis. Therapy for the nephrotic syndrome had not only decreased his body weight and edema, but also the serum creatine kinase and aldolase levels. Although these enzymes increased when he again suffered systemic edema, they decreased to normal levels after normalization of his circulating blood plasma volume by hemodialysis. It is postulated that subclinical neurogenic muscle changes with excess interstitial edema caused the elevation in serum creatine kinase.