Non-traditional risk factors for atherosclerosis were examined in children whose fathers suffered from myocardial infarction up to age 48. Factors examined were hyperinsulinemia, insulin resistance, lipoprotein(a) [Lp(a)], fibrinogen, cardiovascular hyperreactivity, and autonomic nervous system dysfunction. Hyperinsulinemia was present in five cases (9%) and hypoinsulinemia in two. Insulin output following glucose load was significantly higher in obese children compared with controls. There was an increase in Lp(a) alone in 14 cases (24%) and with low density lipoprotein in 6 cases. Increased fibrinogen and positive correlation with insulin abnormality was present in 29% (76% females) (P >0.02). Cardiac hyperreactivity (increased systolic blood pressure) was present in 9% and increased blood pressure and pulse rate in 17%. Holter monitoring pattern was sympathetic in 39% and parasympathetic in 47% of cases. Thus a number of non-traditional risk factors were found to be higher than normal in a relatively large number of children at high risk for atherosclerosis, with 25 children having more than three risk factors.