Plasma cholesterol and triglyceride levels were measured after an overnight fast in 500 consecutively studied 3-mo survivors of myocardial infarction. Virtually all patients under 60 yr of age (95% ascertainment) and a randomly chosen group of older survivors admitted to 13 Seattle hospitals during an 11 mo period were included. A comparison of their lipid values with those of 950 controls demonstrated that 31% had hyperlipidemia. These lipid abnormalities were most commonly found in males under 40 yr of age (60% frequency) and in females under 50 yr of age (60% frequency). Elevation in triglyceride levels with (7.8%) or without (15.6%) an associated elevation in cholesterol levels was three times more common in survivors than a high cholesterol level alone (7.6%). These results raise the possibility that hypertriglyceridemia may be as an important a risk factor for coronary atherosclerosis as hypercholesterolemia. The identification of hyperlipidemic survivors of myocardial infarction provided a unique source of probands for family studies designed to disclose the genetic origin of hyperlipidemia in coronary heart disease.