This study examined the effect of a supervised, aerobic exercise program on change in body weight and composition (multi-site subcutaneous skinfold measures, percent body fat, and lean body weight) of women undergoing adjuvant chemotherapy for breast cancer. Stage II patients with breast cancer (N = 24) were randomized to an exercise treatment group (EG, n = 12) and a control group (CG, n = 12). The EG participated in the individualized Winningham Aerobic Interval Training (WAIT) exercise program with exertional levels set at 60%-85% of maximal heart rate for 20-30 minutes, 3 times per week, for 10-12 weeks. The CG received no exercise treatment, but were asked to continue with their daily activities. Subjects were asked to maintain their customary eating patterns throughout their participation. Data were analyzed using covariate analysis, adjusting for age and pre-test values. Comparisons of pre- and post-test results indicated that exercise had a moderating effect on gain in body fat and altered the subcutaneous body fat profile in both obese (OB) and nonobese (NOB) subjects. Exercising OB subjects showed a greater increase in lean body weight than NOB subjects, indicating an increase in muscle tissue. Results from this study may be useful in designing safe and effective weight-control programs for patients with breast cancer on chemotherapy.