The characteristics and clinical usefulness for aspartate aminotransferase (AST) isoenzyme including apo- and holo-type enzymes were reviewed. The activation effect on mitochondrial- and cytosolic-AST (mAST and cAST) was compared in the presence of PALP, to sera of various diseases such non-alcoholic liver-, heart-, renal, and alcoholic liver diseases. A higher activation by PALP was described on both AST in the sera with ischemic heart disease than liver disease. Significantly higher apo and holo type of serum mAST were found even in patients with alcoholic fatty liver in the early stage of alcoholic liver injury than those in the normal. The mitochondrial injury relates to onset and progression of cellular necrosis so that differential measurement of apo and holo type activities of serum mAST might be useful for early prediction of necrotic diseases.