31P nuclear magnetic resonance (NMR) was used to investigate the resting energy metabolism of the calf muscle in boys with Duchenne's muscular dystrophy. Reductions in the phosphocreatine/adenosine triphosphate (PCr/ATP) and the PCr/Pi ratios were found, but ATP as a fraction of the total mobile phosphorus signal was not reduced, and intracellular pH was normal in the Duchenne muscle. Attempts at quantitation of the NMR signal suggested that the reduced total phosphorus signal seen in the Duchenne muscle was a result of muscle fiber loss only and that the muscle fiber ATP concentration was probably normal in the diseased tissue. An exercise study in one 7-year-old boy with Duchenne's dystrophy demonstrated that the muscle had a normal ability to break down and resynthesize phosphocreatine. Presented here are the first reported trials of the effects of two putative therapeutic agents on energy metabolism determined by NMR in Duchenne's muscular dystrophy.