Intravenous and oral glucose tolerance, as well as insulin response to glucose ingestion and a glucose infusion test, were investigated in 104 male nondiabetic survivors of myocardial infarction under the age of 45 years and in 100 matched control subjects randomly selected from the general population. Reduced oral glucose tolerance and hyperinsulinemic responses to both oral glucose challenge and to a glucose infusion test were present in a substantial number of the young patients. The very low density lipoprotein triglyceride concentration tended to rise progressively with increasing severity of glucose intolerance in both patients and control subjects. The magnitude of the early insulin response during the glucose infusion test, along with the high density lipoprotein cholesterol concentration, correlated inversely and independently with degree and extent of coronary atheromatosis, whereas the low density lipoprotein cholesterol level showed a positive correlation with severity of coronary atheromatosis. The present data argue against the concept of direct atherogenic action of high plasma insulin levels. In contrast, a low and delayed early insulin response might be a marker of enhanced liability to evolution of severe diffuse coronary atheromatosis.