The loss of full-length dystrophin from skeletal muscle leads to the clinical features of Duchenne muscular dystrophy. Both Dp71, a C-terminal dystrophin isoform, and the dystrophin-related protein, utrophin, are present at high levels in many nonmuscle tissues. To investigate the roles of these proteins in nonmuscle tissues, mice were generated null for utrophin, and deficient in all dystrophin isoforms. These mice reach adulthood and do not appear to have any devastating pathology in nonmuscle tissues.