The mdx mouse, an animal model used to study Duchenne muscular dystrophy, has a nonsense mutation in exon 23 of the dystrophin gene which should result in a truncated protein that cannot be correctly localized at the sarcolemma of the muscle fibers. Immunohistochemical staining with antidystrophin antibodies has shown that while most of the muscle tissue is dystrophin‐negative, a small percentage of muscle fibers is clearly dystrophin‐positive and has somehow bypassed the primary nonsense mutation. A sensitive nested polymerase chain reaction‐based examination of dystrophin gene transcripts around the mdx mutation has revealed several alternatively processed transcripts. Four mRNA species skipped the mutation in exon 23, were in‐frame, and could be translated into a shorter but still functional dystrophin protein. Specific tests for these transcripts demonstrated these were also present in normal mouse muscle tissue. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 728–734, 1997.