IN MUSCULAR dystrophy, particularly of the Duchenne or sex-linked type, a number of enzymes generally have elevated levels in the serum. In diseases such as the various kinds of neurogenic muscular atrophy that may be mistaken for muscular dystrophy, enzyme levels are normal. On the other hand, diseases like hepatitis that may show high enzyme levels are readily distinguishable from muscular dystrophy by their symptoms. Thus, the serum enzymes are of great value in diagnosis whenever muscular dystrophy is a possibility. They are also very promising as a tool in research. The enzymes in the serum appear to enter the blood by leakage from damaged muscle cells. The determination of serum enzymes may provide a way of measuring the intensity of the disease process at a given time. If so, the enzymes are useful not only for diagnosis but are essential for studying the development of the disease and