Dystrophin is the protein product of an X-linked locus which is disrupted to yield the phenotypes of Duchenne and Becker muscular dystrophies. Recently an autosomal transcript was identified (Love, D. R., Hill, D. F., Dickson, G., Spurr, N. K., Byth, B. C., Marsden, R. F., Walsh, F. S., Edwards, Y. H., and Davies, K. E. (1989) Nature 339, 55-58) with a carboxyl-terminal sequence similar to dystrophin. We have isolated part of this chromosome 6-encoded cDNA by polymerase chain reaction cloning and expressed it as a recombinant bacterial protein. Antibodies against this recombinant protein detected a large protein that exactly co-migrates with dystrophin yet is detectable in patients suffering from Duchenne and Becker muscular dystrophies. This protein of similar size to dystrophin may play a functional role similar to dystrophin, but unlike dystrophin, the protein is detected in tissues other than muscle and nerve. This newly identified protein is presumably a member of the spectrin/alpha-actinin/dystrophin family of proteins.