In order to elucidate the effects of hypoglycemia on cardiac and skeletal muscle, plasma activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and creatine kinase (CK) were assessed in rabbits with hypoglycemia induced by i.v. injection of insulin. After hypoglycemia lasting for more than 30 min, the plasma levels of ALT, AST and LDH rose significantly in 4 out of 5 rabbits reaching a peak at 24 hr. The plasma activity of CK rose remarkably and reached a peak at 6 hr after insulin injection in all rabbits. These results suggest prolonged hypoglycemia may cause myocardial and/or skeletal muscle damage, which can be ascertained by measuring plasma activities of the related enzymes.