Fabry disease is a lysosomal storage disorder caused by a deficiency of the lysosomal enzyme alpha-galactosidase A (alpha-gal A). This enzyme deficiency leads to impaired catabolism of alpha-galactosyl-terminal lipids such as globotriaosylceramide (Gb3). Patients develop painful neuropathy and vascular occlusions that progressively lead to cardiovascular, cerebrovascular, and renal dysfunction and early death. Although enzyme replacement therapy and bone marrow transplantation have shown promise in the murine analog of Fabry disease, gene therapy holds a strong potential for treating this disease in humans. Delivery of the normal alpha-gal A gene (cDNA) into a depot organ such as liver may be sufficient to elicit corrective circulating levels of the deficient enzyme. To investigate this possibility, a recombinant adeno-associated viral vector encoding human alpha-gal A (rAAV-AGA) was constructed and injected into the hepatic portal vein of Fabry mice. Two weeks postinjection, alpha-gal A activity in the livers of rAAV-AGA-injected Fabry mice was 20-35% of that of the normal mice. The transduced animals continued to show higher alpha-gal A levels in liver and other tissues compared with the untouched Fabry controls as long as 6 months after treatment. In parallel to the elevated enzyme levels, we see significant reductions in Gb3 levels to near normal at 2 and 5 weeks posttreatment. The lower Gb3 levels continued in liver, spleen, and heart, up to 25 weeks with no significant immune response to the virus or alpha-gal A. Also, no signs of liver toxicity occurred after the rAAV-AGA administration. These findings suggest that an AAV-mediated gene transfer may be useful for the treatment of Fabry disease and possibly other metabolic disorders.