To elucidate the nature of lipid defects in patients with diabetes mellitus (DM) concurrent with acute myocardial infarction (MI), the study was undertaken to examine the serum concentrations of total cholesterol, triglycerides, alpha- and beta-lipoproteins with DM in the presence of acute MI. 40 non-diabetic patients with acute MI, 23 diabetics with postinfarct cardiosclerosis, and 17 non-insulin-dependent diabetics without signs of coronary atherosclerosis. Urinary epinephrine and norepinephrine excretion was additionally determined in the acute period and 3-4 weeks after therapy. Homogeneous lipid metabolic parameters were found in CHD patients with and without DM and when transient hyperglycemia developed. The patients with acute MI exhibited some increase in lipid consumption to satisfy the energy need for the cardiovascular system, this being true for triglycerides in DM patients. The DM patients who showed low triglyceride levels had more frequently transmural MI and MI complicated with heart failure. Obesity and familial histories of DM and CHD in DM patients with acute MI were ascertained to be accompanied by reduced serum alpha-lipoprotein concentrations.