The decrease in intracellular creatine concentration in Duchenne muscular dystrophy may contribute to the deterioration of intracellular energy homeostasis and may thus be one of the factors aggravating muscle weakness and degeneration. Oral creatine supplementation should have potential in alleviating the clinical symptoms. To test this hypothesis, creatine was orally administered over a period of 155 days to a 9-year-old patient with Duchenne muscular dystrophy. In accordance with previous investigations on normal subjects and trained athletes, the patient experienced improved muscle performance during creatine supplementation. Further evidence supporting this hypothesis derived from plasma creatine kinase and lactate dehydrogenase activities and repeated 31P magnetic resonance spectroscopy of the gastrocnemius muscle. These preliminary observations indicate a potential role for creatine supplementation in the symptomatic therapy of patients with muscle disease.