DUCHENNE progressive muscular dystrophy is a lethal and common X-linked genetic disease1 caused by the absence of dystrophin2,3, a 427K protein encoded by a 14 kilobase transcript4. Two approaches have been proposed to correct the dystrophin deficiency in muscle. The first, myoblast transfer therapy, uses cells from normal donors5-7, whereas the second involves direct intramuscular injection of recombinant plasmids expressing dystrophin8. Adenovirus is an efficient vector for in vivo expression of various foreign genes9-13. It has recently been demonstrated that a recombinant adenovirus expressing the lac-Z reporter gene can infect stably many mouse tissues, particularly muscle and heart12,13. We have tested the ability of a recombinant adenovirus, containing a 6.3 kilobase pair Becker-like dystrophin complementary DNA14 driven by the Rous sarcoma virus promoter to direct the expression of a 'minidystrophin' in infected 293 cells and C2 myoblasts, and in the mdx mouse15,16, after intramuscular injection. We report here that in vivo, we have obtained a sarcolemmal immunostaining in up to 50% of fibres of the injected muscle.