β-Glucuronidase injected i.v. into newborn mucopolysaccharidosis VII mice was cleared from the circulation in less than 1 h and taken up by tissues in a distribution corresponding to the location of the mannose 6-phosphate receptor. One h after a 3.5-mg/kg 0-glucuron-idase injection, β-glucuronidase levels were equal to or greater than normal in every organ examined with the exception of the brain, where 31% normal activity was present. Enzyme was detectable histochemically in the major sites of pathology for mucopolysaccharidosis VII including bone, brain, heart, and fixed tissue macrophages. The half-life of recombinant β-glucuronidase activity in various organs of injected mucopolysaccharidosis VII mice was 1.5 to 4.5 d. These studies show that recombinant 0-glucuronidase administered to newborn mice reaches the sites of clinically important storage in murine mucopolysaccharidosis VII.