Children starting their schooling were given a questionnaire asking about the occurrence of premature (before 50 years of age in men, 55 years in women) coronary heart disease (CHD) in first degree relatives. 1,920 of 2,069 questionnaires were answered, 140 of the 7-year-old children were reported to have a first degree relative with premature CHD, 84 of these 140 families agreed to participate in our study. In 79 of the 84 families both the child and the parent at 'high risk' were tested. In the initial test 19 of 84 children had total cholesterol (TC) levels above the 95th percentile (greater than 5.35 mmol/l). In the repeat test 12 of the 19 TC tests remained abnormal and all 12 also had LDL-cholesterol (LDL-C) levels above the 95th percentile (greater than 3.40 mmol/l). None had abnormal HDL-cholesterol or triglyceride levels. Among the high risk parents, 12 of 79 had abnormal initial blood lipid tests. In the repeat test 10 parents had both TC and LDL-C levels above the 95th percentile. In five families both the child and the parent had abnormal TC and LDL-C levels. In conclusion, a considerable proportion of children and parents with family histories of premature CHD have TC and LDL-C concentrations above the 95th percentile (in the present study, about 40 individuals in 140 high-risk families, if the parent and child considered at high risk all had agreed to participate). Prevention of heart disease should begin in childhood when patterns of life-style are developed. Identification by obtained family histories as in the current study may be a method of choice.