Serum cholesterol, triglycerides and high-density lipoprotein (HDL) cholesterol were determined in 56 male survivors of myocardial infarction (MI), suffered 6--20 months earlier, and in 82 healthy age- and sex-matched controls. The mean age of both groups was 39 years. Total serum cholesterol was within normal limits in both groups, whereas HDL cholesterol was considerably lower and triglycerides remarkably elevated in MI patients compared with the controls. Judging from previous and present data, low HDL cholesterol seems to be a coronary risk factor as such. This study indicates that low HDL cholesterol, and especially a low HDL cholesterol/total cholesterol ratio, may be stronger coronary risk factors than total serum cholesterol alone. Because HDL cholesterol and triglycerides were inversely correlated, these results also emphasize the importance of serum triglycerides as a risk factor for coronary heart disease.