Serum high density lipoprotein is increasingly recognized as a negative risk for cardiovascular disease. The distribution and interrelationship of serum lipids, lipoproteins, anthropometric measurements and blood pressures were determined in some 5,000 children. Children had mean +/- S.D. alpha-lipoprotein cholesterol levels (mg/100 ml) of 36 +/- 15 at birth, 51 +/- 22 at 6 mo, 53 +/- 18 at 1 yr, 60 +/- 19 at preschool age (2 1/2-5 1/2 yr) and 68 +/- 22 at school age (5-14 yr), reflecting a sharp increase in alpha-lipoprotein between birth and school-age years, when these levels remained relatively stable through age 14. Although white children tended to have higher levels of total cholesterol and alpha-lipoprotein at birth than black children, during childhood this trend was reversed and the differences were pronounced in school-age children (p less than 0.0001). Unlike in adulthood, boys had slightly higher levels of alpha-lipoprotein than girls. The alpha-lipoprotein was negatively correlated with pre-beta-lipoprotein and to a lesser extent with beta-lipoprotein classes. There was an inverse relationship between alpha-lipoprotein and obesity with a consistently significant relationship (p less than 0.01) in older children (10-14 yr). Children with higher levels of alpha-lipoprotein have lower levels of blood pressure, beta-lipoprotein and a lower obesity index.