In order to examine the relationship between certain risk factors for atherosclerosis and family history of myocardial infarction, we compared a group of children (n=51) whose parents had survived myocardial infarction (n=34) with a control group of children (n=90) with a negative family history of atherosclerosis (62 parents). The study revealed a surprising fact that 26.7 % of control children had hypercholesterolaemia compared to 15.7 % incidence in "risk" children. "Risk" children differed from the controls most in the apo-A-l levels and a higher risk index expressed by the proportion of apo-B:apo-A-l (1.22, 1.34 g/1, p=0.001, 0.58, 0.46, p=0.05, respectively). Since the most frequent primary hyperlipoproteinaemia in myocardial infarction families was familial combined hyperlipoproteinaemia, we assume that this condition may be presented in affected children by an unfavourable proportion of apolipoproteins of the lipoprotein classes.