Two recombinant human agalsidase preparations are available for treatment of Fabry disease. We assayed urinary GL-3 (uGL-3) concentration in seronegative and seropositive patients receiving agalsidase beta (1mg/kg). Antibody formation and residual enzyme activity were strongly correlated. Normalization of uGL-3 was achieved more efficiently in seronegatives. But different from previous reports, reduction of uGL-3 level was observed in some seropositive patients.