The effect of aerobic exercise on total cholesterol (TC), high-density lipoprotein (HDL), apolipoprotein B (Apo B), apolioprotein A-I (Apo A-I), and percent body fat in adolescent females was studied. The control subjects (n=86) were volunteers who had completed a physical education class at least six months prior to the commencement of the study, and the treatment (n=79) subjects were volunteers who were newly enrolled in the investigator's physical education classes. All subjects were pretested and posttested on the dependent variables. The treatment subjects participated in a 12-week aerobic exercise program during their physical education classes. Their TC, Apo B, and body fat levels decreased significantly while their HDL and Apo A-I levels did not change. The control group's TC and HDL decreased with no changes in other varieties. When the treatment and control groups were compared, the treatment group had significantly lower body fat and Apo B levels and higher HDL. Findings of this study support the conclusion that modification of Apo B and body fat, risk factors for cardiovascular disease (CVD), may be possible during adolescent years through participation in aerobic exercise. However, longitudinal studies are necessary to determine if adolescent CVD risk modification, involving aerobic exercise, can reduce future CVD risk. (Author/IAH)