Histological, histochemical and morphometric characteristics of diaphragm muscles from mdx and control mice were compared with those of hindlimb muscles [extensor digitorum longus (EDL), tibialis anterior (TA) and soleus (SA) muscles]. In contrast to mdx limb muscles, regeneration after muscle necrosis does not restore diaphragm muscle structure. In mdx mice at 270 days of age, 70-80% of fibres in hindlimb muscles had central nuclei, compared with only 35% in diaphragm muscle. At 270 days of age, mdx diaphragm muscle was characterized by perimysial and endomysial fibrosis; this latter feature was absent from mdx hindlimb muscles. Fibre diameter remained smaller than the control in mdx diaphragm muscle. We suggest that the similarity in muscle pathology between the diaphragms of mdx mice and in patients suffering from Duchenne muscular dystrophy (DMD) makes these an appropriate model for DMD, since respiratory failure is the leading cause of death in DMD patients.