Muscle and serum CPK electrophoretic pattern and serum GOT electrophoretic pattern were studied in Duchenne type, limb-girdle type and distal congenital type muscular dystro- phies. Muscle CPK isoenzyme pattern usually did not show significant changes. In 2 cases a fetal-like pattern was observed. Serum CPK isoenzyme pattern showed in some cases only the MM type. In other cases MB type was found in addition to MM type. Serum electrophoresis zone of GOT displayed in some cases only the cytoplasmic isoenzyme. Other cases showed mitochondrial isoenzyme in addition to the cytoplasmic type. The latter was predominant. GOT mitochondrial isoenzyme and CPK MB isoenzyme were found in serum in the early stages of the disease. These results suggest that a relationship may intercur between the pathological changes in the muscle in early muscular dystrophy and the presence in serum of GOT mitochondrial isoenzyme and CPK MB isoenzyme.