The results presented here demonstrate that there is a major abnormality of high and low energy phosphate metabolism in muscle following peripheral nerve damage. Using 31-phosphorus magnetic resonance spectroscopy the changes in phosphocreatine, adenosine triphosphate, inorganic phosphate and metabolites of membrane metabolism could be observed in vivo in human subjects. The data indicate that there may be a metabolic myopathy in the muscle cells after nerve injury. Further, the metabolic changes did not always return to the control level, indicating a persistence of the abnormality. This failure of the metabolic function of the cells may be important in determining the ultimate outcome of peripheral nerve surgery.