In December 2000, a phase 3 double-masked, placebo-controlled, multicenter trial was initiated to assess the safety and efficacy of treatment with recombinant α-L-iduronidase (Aldurazyme [BioMarin Pharmaceutical Inc, Novato, California; and Genzyme Corporation, Cambridge, Massachusetts]) in those with MPS I.15 In this trial, 45 patients were enrolled at 5 sites in the United States, Europe, and Canada. At each study site, institutional ethic committee approval was obtained. The enzyme (α-L-iduronidase) or placebo was administered intravenously once each week for 26 weeks at a dosage of 0.58 mg/kg body weight. At the end of the double-masked phase, all 45 patients entered an open-label extension study. Patients enrolled in the study had MPS I with less than 10% iduronidase activity and were at least aged 5 years and able to perform the primary efficacy assessments. To be included, forced vital capacity had to be less than 80% of the predicted normal value and patients had to be able to perform a 6-minute walk test. At the study site in Mainz, 9 patients were included. Assignment of the patients to the MPS I subtypes (Scheie, Hurler-Scheie, or Hurler) was based on clinical findings. An 8-year-old patient died during the study period because of myocarditis unrelated to ERT. His data are not included in the present report. The remaining 3 male and 5 female patients (mean age, 25 years at study enrollment; age range, 7-43 years) were followed up with ERT for 4 years. Ophthalmological assessments were performed annually. However, patients with visual complaints were seen as required. The examination included monocular assessment of best-corrected and uncorrected VA using Snellen charts, measurement of intraocular pressure by either Goldmann applanation tonometry or digital palpation, slitlamp examination of the anterior segment (model BQ 900; Haag Streit, Köniz, Switzerland), and direct and indirect ophthalmoscopy. Corneal clouding, if present, was graded as mild, moderate, or severe. In a few patients, static 30° perimetry was performed (Octopus G2 perimeter; Interzeag AG, Schlieren, Switzerland).