Genetic defects of lysosomal hydrolases result in severe storage diseases and treatments based on enzyme replacement have been proposed. In mice lacking beta-glucuronidase, which develop a disease homologous to human mucopolysaccharidosis type VII (MPS VII, sly syndrome), we have used autologous implants of genetically-modified cells for the continuous in vivo production of the enzyme. A retroviral vector containing the human beta-glucuronidase cDNA under the control of the mouse phosphoglycerate kinase promoter was used to infect primary skin fibroblasts, bone marrow cells, or myoblasts from mutant MPS VII animals. The fibroblasts were embedded into collagen lattices and reimplanted into the peritoneal cavity of recipient MPS VII mice. All animals, when analysed 10 to 155 days later, expressed beta-glucuronidase from the vascularised neo-organs that developed after implantation, and accumulated the enzyme in their tissues. A complete disappearance of the lysosomal storage lesions was observed in their liver and spleen. This procedure has been scaled up for long term lysosomal enzyme delivery in dogs. The bone marrow cells were used for partial hematopoietic reconstruction of sublethally irradiated MPS VII mice. Five months after gene transfer, animals in which under 5% of genetically-modified hematopoietic cells were detected in the spleen showed a drastic reduction of lysosomal storage lesions in the liver and spleen. Genetically-modified myoblasts were transplanted into injured muscles, where they participated in the regeneration of a significant proportion of muscle fibers. Enzyme secretion and liver uptake were observed for at least one month.(ABSTRACT TRUNCATED AT 250 WORDS)