Aim: Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) is a lysosomal storage disease caused by a deficiency of the enzyme N-acetylgalactosamine 4-sulphatase (ASB)-. Enzyme replacement therapy with recombinant human ASB (rhASB) has been studied in a randomized, double-blind, twodose (0.2 and 1.0mg/kg/week) phase I/II study (n = 7) followed by an open-label single dose (1.0mg/kg/week) extension study. We report the pharmacokinetic profile of rhASB and the impact of antibody development. Methods: Pharmacokinetic analysis was performed at weeks 1, 2, 12, 24, 83, 84 and 96. Infusions were administered over 4 hours using a ramp-up protocol. Plasma ASB and rhASB antibody concentrations and urine glycosaminoglycan (GAG) concentrations were determined. Results: The area under the plasma concentration-time curve (AUC0-t) for the high-dose group increased from week 1 to week 2, but remained unchanged at weeks 12 and 24. A large difference in mean AUC0-t was observed between the low-and high-dose groups. Pharmacokinetic results at weeks 83, 84 and 96 were similar to those at week 24. Six patients developed antibodies to rhASB. One patient developed high antibody levels in combination with a high ASB concentration, while a second patient also developed high antibody levels with undetectable ASB concentrations. Antibodies from the second patient blocked detection of ASB. By week 72, antibody levels had decreased in all patients. The high-dose rhASB produced a more rapid and greater percentage reduction in urinary GAG concentrations than the lower dose (70% versus 55% at 24 weeks). Antibody levels did not appear to influence urinary GAG concentrations. Conclusion: Pharmacokinetic parameters appear to be independent of the duration of treatment and are not linear between the 0.2 and 1.0 mg/kg/week doses. Antibodies to rhASB develop in most patients, but their concentration decreases over time. Antibody formation may influence pharmacokinetic parameters during the early phases of treatment, although it appears to have limited impact on biochemical efficacy. Aim: Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) is a lysosomal storage disease caused by a deficiency of the enzyme N-acetylgalactosamine 4-sulphatase (ASB) -. Enzyme replacement therapy with recombinant human ASB (rhASB) has been studied in a randomized, double-blind, twodose (0.2 and 1.0 mg / kg / week) phase I / II study (n = 7) followed by an open-label single dose rhASB and the impact of antibody development. Methods: Pharmacokinetic analysis was performed at weeks 1, 2, 12, 24, 83, 84 and 96. Infusions were administered over 4 hours using a ramp-up protocol. Plasma ASB and rhASB antibody concentrations and Results: The area under the plasma concentration-time curve (AUC0-t) for the high-dose group increased from week 1 to week 2, but remained unchanged at weeks 12 and 24. A large difference in mean AUC0-t was observed between the low-and high-dos e groups. Pharmacokinetic results at weeks 83, 84 and 96 were similar to those at week 24. Six patient developed antibodies to rhASB. One patient developed high antibody levels in combination with a high ASB concentration, while a second patient also developed high antibody levels Antibodies from the second patient blocked detection of ASB. By week 72, the antibody levels had decreased in all patients. The high-dose rhASB produced a more rapid and greater percentage reduction in urinary GAG concentrations than the lower dose (70 % versus 55% at 24 weeks). Antibody levels did not appear to influence urinary GAG concentrations. Conclusion: Pharmacokinetic parameters appear to be independent of the duration of treatment and are not linear between the 0.2 and 1.0 mg / kg / week doses. Antibodies to rhASB develop in most patients, but their concentration decreases over time. Antibody formation may influence pharmacokinetic parameters during the early phases oftreatment, although it appears to have limited impact on biochemical efficacy.