Retroviral vectors were used to transfer genes efficiently into rat and dog myoblasts in primary cultures under conditions which permitted the transduced myoblasts to differentiate into myotubes expressing the transferred genes. The transduced myotubes expressed normal markers of differentiation and were morphologically indistinguishable from uninfected myotubes. Retroviral vector-mediated gene transfer was also used to correct a genetic enzyme deficiency in mutant canine muscle cells.