Gaucher disease is the most frequent lysosomal storage disease and the most prevalent genetic disease among the Ashkenazi Jews (q approximately 0.047). The disease results from inherited defects of acid beta-glucosidase and the accumulation of the substrate, glucosylceramide, in cells of monocyte/macrophage origin. The therapeutic response to macrophage-targeted (alpha-mannosyl-terminated) alglucerase (Ceredase, at 60 to 15 IU/kg every 2 weeks) was analyzed in 33 patients (age range, 2 to 63 years; 15 splenectomized) with extensive Gaucher disease over periods of 6 to 24 months. The efficacy of several different doses and dosage reductions was evaluated. In patients with anemia (n = 30) and/or thrombocytopenia (n = 19), hemoglobin levels and platelet counts increased by 0% to 178% and 15% to 155%, respectively, within 3 to 12 months. In patients with splenomegaly (n = 17) and/or hepatomegaly (n = 28), liver and spleen volumes decreased in 6 months from 7% to 64% and 8% to 84% by 12 months, respectively. Hematologic and visceral improvements were noted at any doses between 60 and 15 IU/kg every 2 weeks. Furthermore, these positive initial therapeutic responses were persistent throughout therapy, with doses reduced by 50%. Pulmonary Gaucher disease did not improve clinically in 3 patients. Unrelated cirrhotic (n = 2), cholestatic (n = 1), or renal disease (n = 1) did not influence the rate of patient improvement. Two of five patients who developed serum antibodies against alglucerase during the first 6 to 12 months of therapy had mild antibody reactions. This study shows similar regression of clinical Gaucher disease manifestations with enzyme therapy, using doses between 30 and 60 IU/kg every 2 weeks. Therapeutic efficacy was not diminished after 50% to 75% dose reductions or in the presence of anti-enzyme antibodies.