An exploratory, open-labeled study of patients with Pompe disease, who have previously received Myozyme (alglucosidase alfa) treatment, to evaluate the efficacy, safety and clinical benefit of 2 Immune Tolerance Induction (ITI) regimens in combination with Myozyme. Eligible patients who are currently receiving Myozyme therapy will be enrolled into the study, and will be followed for a minimum of 18 months on-study (a 6-month ITI treatment module and a 12-month follow-up module on Myozyme alone). Eligible patients will be followed for a minimum of 18 months on treatment or, if a patient is <6 months of age at the time of enrollment, until the patient is 2 years of age. Both cross-reacting immunologic material (CRIM)-negative and CRIM-positive patients can be eligible for Regimen A depending if they meet the required criteria. Regimen B however, is limited to CRIM-negative patients.