Dystrophin is a cytoskeletal protein not directly participating the myosin-actin contractile apparatus in muscle. The loss of dystrophin leads to Duchenne muscular dystrophy. It is well-established that contractility is reduced in dystrophin-null muscle. Surprisingly, little is known about the influences of dystrophin-deficiency on the passive properties of muscle. We hypothesize that the loss of dystrophin alters the passive properties of the skeletal muscle. To test this hypothesis, we examined the passive properties of the extensor digitorum longus (EDL) muscle from normal BL10 and dystrophin-null mdx mice