A replication-defective recombinant adenoviral vector containing E. coli lacZ gene was injected into the right biceps brachii muscles of transgenic mice carrying mutant human Cu/Zn superoxide dismutase (SOD1) gene and non-transgenic wild-type mice at 27 weeks of age. Although the transgenic mice showed remarkable neurogenic muscular changes and a marked motor neuron loss in the anterior horn of spinal cord, the lacZ gene was widely expressed in all the injected muscles of transgenic mice as well as of wild-type mice at 7 days after the injection. In one transgenic and two wild-type mice, the lacZ gene expression was first detected in a few motor neurons of right lower cervical cord (C5-C6). These results demonstrate that an adenovirus-mediated foreign gene is transferred and expressed in skeletal muscles both of normal and transgenic mice model for familial amyotrophic lateral sclerosis (FALS), and also, in the spinal motor neurons, may be transferred by retrograde transport from innervated muscles.