Tai Chi Chuan (TCC; shadow boxing) is a traditional Chinese conditioning exercise. To evaluate its beneficial effect on cardiorespiratory function, 21 male and 20 female TCC practitioners, ranging in age from 50 to 64 years, voluntarily participated in this study. The control group comprised 23 male and 26 female sedentary subjects. Breath-by-breath measurement of the cardiorespiratory function was obtained during the incremental exercise of leg cycling. At the maximal exercise level, the oxygen uptake (VO2), O2 pulse and work rate of the TCC group were significantly higher than the respective values of the control group (p < 0.01). At the ventilatory threshold, the TCC group also showed a higher VO2, O2 pulse and work rate (p < 0.05). The results imply that TCC training may be beneficial to the cardiorespiratory function of older individuals. To estimate the exercise intensity of TCC, heart rate (HR) was monitored in 15 men and 15 women while they performed the classical Yang TCC. During the steady-state performance of TCC, the mean HR was 130 +/- 14 bpm for men and 127 +/- 13 bpm for women. The mean HR during TCC exceeded 70% of their HRmax. Our data substantiate that TCC is aerobic exercise of moderate intensity, and it may be prescribed as a suitable conditioning exercise for the elderly.