The protective effects of L-arginine, in combination with L-lysine on lipid metabolism were examined against isoproterenol-induced myocardial infarction in rats. The levels of cholesterol, triacylglycerols and free fatty acids were estimated both in serum and the myocardial tissue. The levels of LDL- and HDL-cholesterol in serum and phospholipids in the myocardial tissues were also estimated in the normal and experimental rats. The rats administered isoproterenol (150 mg kg(-1) daily, intraperitoneally) showed significant changes in the lipid components. Prior oral treatment with L-arginine (250 mg kg(-1) daily) along with L-lysine (5 mg kg(-1) daily) in alleviating isoproterenol-induced biochemical disturbances with respect to lipid metabolism has been the hallmark of the study.