• Weakness of the proximal muscle groups developed in six uremic patients, five men and one woman, while receiving hemodialysis. All showed roentgenographic evidence of renal osteodystrophy. Partial to complete recovery of strength followed subtotal parathyroidectomy in four patients. All patients had normal levels of creatine phosphokinase. Electrodiagnostic testing showed features of both "myopathic" and denervating processes on coaxial needle exploration and normal to slowed nerve conduction. Muscle biopsy specimens in four patients showed type 2 fiber atrophy with no evidence of necrosis, phagocytosis, regeneration, or vasculitis. The pathogenesis of proximal muscle weakness in uremia is uncertain but may be related to secondary hyperparathyroidism or osteodystrophy.