Summary GOT isoenzymes of sera and muscle tissue from normal subjects and those with various myopathies have been analyzed by agar gel electrophoresis. Serum was found to contain only one fraction (GOT I) whereas muscle and other tissues contained variable amounts of 2 fractions (GOT I and II). The serum from persons with muscular dystrophy contained only an increased activity of GOT I fraction. Since this fraction is derived from the soluble sarcoplasm of muscle it implies that the mitochondrial fraction (GOT II) is retained and that mitochondria are not undergoing rapid breakdown in the myopathies. The proportional distribution of the 2 GOT isoenzymes in skeletal muscle tissue is unchanged in subjects with childhood muscular dystrophy and in other myopathies. GOT shows no difference in its pattern in skeletal muscle from different sites and only minor variations in certain other organs such as heart, liver, spleen, lung and kidney.