The effect of a 10-week aerobic interval-training cycle ergometer protocol on the functional capacity (VO2Lmax) of 45 women receiving chemotherapy for treatment of Stage II breast cancer was studied. Subjects were stratified by baseline functional capacity (+/- 1 MET) and randomized to experimental (EX), placebo (PL), and control (CO) groups. EX subjects completed a 10-week, 3 times/week exercise training program; PL subjects participated in 10 weeks of nonaerobic stretching and flexibility exercises; the CO group maintained normal activities. The EX group showed significant, p less than .05, improvement on pre- to posttest VO2Lmax as well as workload and test time compared to the PL and CO groups. The interval-training exercise intervention was effective in improving the functional capacity of Stage II breast cancer patients on adjuvant chemotherapy.