We studied four patients with muscle necrosis associated with acute renal failure to evaluate the diagnostic value of the bone scan in this disease. The illness followed carbon monoxide poisoning in two patients, acute physical exertion in one and contaminated intramuscular injection in the other. Whole-body rectilinear bone scans using technetium 99m-methyldiphosphonate were done. In all patients, increased muscle labelling at the regions of suspected muscle injury was showed, and in one, it was after normalization of serum muscle enzyme levels. In one patient, the bone scan was rechecked 8 months later and showed no residual abnormality. Above all, the site and precise extent of muscle injury could be detected and the degree of muscle labelling seemed to correlate with the severy of muscle injury. These findings suggest that isotope scanning may be useful in the diagnosis of patients with acute muscle necrosis.