We examined the effects of weight loss induced by diet-orlistat (DO) and diet-orlistat combined with exercise (DOE) on maximal work rate production (Wmax) capacity in obese patients. Total of 24 obese patients were involved in this study. Twelve of them were subjected to DO therapy only and the remaining 12 patients participated in a regular aerobic exercise-training program in addition to DO therapy (DOE). Each patient performed two incremental ramp exercise tests up to exhaustion using an electromagnetically-braked cycle ergometer: one at the onset and one at the end of the 4th week. DOE therapy caused a significant decrease in total body weight: 101.5±17.4 kg (basal) vs 96.3±17.3 kg (4 wk) associated with a significant decrease in body fat mass: 45.0±10.5 kg (basal) vs 40.9±9.8 kg (4 wk). DO therapy also resulted in a significant decrease of total body weight 94.9±14.9 kg (basal) vs 91.6±13.5 kg (4 wk) associated with small but significant decreases in body fat mass: 37.7±5.6 kg (basal) to 36.0±6.2 kg (4 wk). Weight reduction achieved during DO therapy was not associated with increased Wmax capacity: 106±32 W (basal) vs 106±33 W (4 wk), while DOE therapy resulted in a markedly increased Wmax capacity: 109±39 W (basal) vs 138±30 W (4 wk). DO therapy combined with aerobic exercise training resulted in a significant reduction of fat mass tissue and markedly improved the aerobic fitness and Wmax capacities of obese patients. Considering this improvement within such a short period, physicians should consider applying an aerobic exercise-training program to sedentary obese patients for improving their physical fitness and thereby reduce the negative outcomes of obesity.