A full-length cDNA clone encoding the lysosomal hydrolase alpha-L-fucosidase was cloned into two retroviral vectors, one using the human cytomegalovirus immediate-early promoter for expression, and the other, the retroviral long terminal repeat (LTR). High-titer amphotropic virus was produced for both constructs by infection of PA317 cells, and used to efficiently transduce the alpha-L-fucosidase gene into both human and canine fucosidosis fibroblasts. This resulted in correction of the alpha-L-fucosidase enzyme deficiency characteristic of these fibroblasts. The high levels of recombinant enzyme produced corrected the degradative defect normally seen in these cells, enabling them to catabolize efficiently the accumulated storage product present in lysosomes. Therefore, these retroviral constructs should allow us to start evaluating the value of gene therapy in treating the central nervous system pathology associated with fucosidosis and other lysosomal storage disorders in humans, using a canine model of fucosidosis.