Forty-three male patients with myocardial infarction, severe angiographic coronary lesions, high or normal low density lipoprotein (LDL) cholesterol serum levels, and without other risk factors for coronary heart disease were selected. In all patients high density lipoprotein (HDL) cholesterol and HDL-cholesterol/total cholesterol ratio were significantly lower than in the control group; in particular, the ratio was below 0.240 which was the median value of normal subjects. Six patients with total cholesterol and LDL-cholesterol below 5.16 and 3.35 mmol/l respectively, had low serum levels of HDL-cholesterol; in 4 of them the value of this risk factor was below 0.9 mmol/l; 2 of 6 patients had a lipoprotein (a) serum concentration above 0.3 g/l but not a premature myocardial infarction or a clinical history of coronary heart disease. Our data confirm that HDL-cholesterol/total cholesterol ratio could be a better marker of coronary heart disease than HDL-cholesterol, total cholesterol or LDL-cholesterol and suggest the importance to check HDL-cholesterol serum levels also in subjects without risk factors for atherosclerotic disease.