The apolipoprotein and lipid profiles were investigated in 22 female gymnasts, 20 girl swimmers, and 12 controls. The average age of all groups was about 12 years, and the girls were matched for sexual development, i.e., breast development stage m = 1 or m = 2. The gymnasts appeared to have the highest level of HDL cholesterol and the highest HDL cholesterol / total cholesterol, HDL cholesterol / LDL cholesterol and HDL cholesterol/apo A-I ratios in comparison to both the swimmers and the control group. The swimmers had the highest level of apo A-I, but a lipid profile similar to that of the controls. It is concluded that in children, as in adults, regular physical activity affects the lipid and apolipoprotein profiles. In addition, it appears that the apolipoproteins discriminate between trained and nontrained subjects as well as (apo B) or better (apo A-I) than the lipid components of the corresponding lipoproteins (LDL cholesterol or HDL cholesterol).