The Western blotting technique was used to detect parvalbumin and S-100 protein in muscles from 10 Duchenne muscular dystrophy (DD) patients, 13 patients with other muscle diseases and 5 age-matched healthy subjects. DD muscles were found to contain decreased amounts of parvalbumin and the S-100 protein. The parvalbumin level did not relate to the age of the patients and the stage of the disease. The S-100 protein decreased progressively with the age of the patients. In a very advanced DD case the S-100 protein was present in trace amounts. In other primary myopathies, including Becker dystrophy, and neurogenic muscular atrophy both parvalbumin and S-100 protein levels were similar to that observed in healthy subjects. The decrease in the amount of both calcium binding proteins may contribute to the elevation of free intracellular Ca2+ level in the sarcoplasm of dystrophic muscle and would result in abnormalities in processes regulated by these proteins. The mechanism(s) responsible for the decrease of parvalbumin and S-100 protein in DD muscles are discussed.