There are now several forms of variants of myopathy associated with absent or deficient lysosomal alpha glucosidase. The classical Pompe's disease, type II glycogenosis, has an absence of the enzyme in all tissues except the kidney, and the heart is prominently involved. A juvenile form, i.e., later onset, presents simulating muscular dystrophy. Here, too, the enzyme is absent, but the heart is not clinically involved. This constellation can be seen in older children and adults where the myopathy is predominant. There is also a form of myopathy where the enzyme is markedly lowered and the Km 1/2 the normal. We are trying to isolate the enzyme from the urine to perform genetic studies and in order to use this source of enzyme to better characterize the enzyme.