Duchenne muscular dystrophy (DMD) is the most common and the most severe of the muscular dystrophies in man¹. It is inherited as an X-linked recessive trait¹ and is characterized by ongoing necrosis of skeletal muscle fibres with regeneration and eventually fibrosis and fatty infiltration². Although the gene and gene product which are defective in DMD have recently been identified^3–5, the pathogenesis of the disease is still poorly understood. A myopathy has been described in the dog^6–8 which has been shown to be inherited as an X-linked trait⁹ and which is therefore a potential model of the human disease. We have studied the phenotypic expression of the disease, canine X-linked muscular dystrophy (CXMD), and have examined the molecular relationship between it and DMD. We report here that dogs with CXMD faithfully mimic the phenotype of Duchenne muscular dystrophy and that they lack the Duchenne gene transcript and its protein product, dystrophin.