Autosomal recessive deficiency of lysosomal acid maltase (GAA) or glycogen storage disease type II (GSDII) results in a spectrum of phenotypes including a rapidly fatal infantile disorder (Pompe's), juvenile, and a late-onset adult myopathy. The infantile onset form presents as hypotonia with massive accumulation of glycogen in skeletal and heart muscle, with death due to cardiorespiratory failure. Adult patients with the slowly progressive form develop severe skeletal muscle weakness and respiratory failure. Particle bombardment is a safe, efficient physical method in which high-density, subcellular-sized particles are accelerated to high velocity to carry DNA into cells. Because it does not depend on a specific ligand, receptor, or biochemical features on cell surfaces, particle-mediated gene transfer can be readily applied to a variety of systems. We evaluated particle bombardment as a delivery system for therapy of GSDII. We utilized a vector carrying the CMV promoter linked to the human GAA cDNA. Human GSDII cell lines (fibroblasts and lymphoid) as well as ex vivo with adult-onset peripheral blood cells (lymphocytes and monocytes) were transiently transfected by bombardment with a Helios gene gun delivering gold particles coated with the GAA expression plasmid. All cell types showed an increase in human GAA activity greater than 50% of normal activity. Subsequently, GAA -/- mice were treated every 2 weeks for 4 months by particle bombardment to the epidermis of the lower back and hind limbs. Muscle weakness in the hind and forelimbs was reversed. These data suggest that particle delivery of the GAA cDNA by the Helios gene gun may be a safe, effective treatment for GSDII.