Pompe disease is a rare autosomal recessive myopathy due to the deficiency of lysosomal acid alpha-glucosidase. Clinical phenotypes range from the severe classic infantile form (hypotonia and hypertrophic cardiomyopathy), to milder late onset forms (skeletal myopathy and absence of significant heart involvement). Enzyme replacement therapy with recombinant human alpha-glucosidase derived from either rabbit milk or Chinese hamster ovary cells has been introduced and is undergoing clinical trials. Reported is a long-term follow-up of 3 Pompe patients presenting without cardiomyopathy, treated with recombinant human alpha-glucosidase derived from Chinese hamster ovary cells. This study suggests that enzyme replacement therapy can lead to significant motor and respiratory improvement in the subgroup of patients who start the therapy before extensive muscle damage has occurred. The recombinant enzyme derived from Chinese hamster ovary cells, administered at doses significantly higher than previously reported, appears to have the same safety as the drug derived from rabbit milk.