BACKGROUND: Although maximal exercise stress tests are widely used in the athletic and medical fields, studies on professional soccer players are few. The purpose of our study is to observe the cardiopulmonary response to maximal exercise loading and the AT in professional soccer players. METHODS: Maximal exercise stress tests were carried out by a ramp protocol using a treadmill on 20 professional soccer players with a mean age of 25.2 years and with over 10 career years. The tests were also done on 21 college students majoring in physical education with a mean age of 19.4 years, which served as the control group. The AT was determined by the V-slope method. RESULTS: In the players, the VO2 max, VCO2 max and O2 pulse max were significantly larger than those in the control group, and the HR max was smaller for their ages. The VE max, VT max and RP max showed not much difference between the 2 groups but the VE max/VO2 max and VE max/VCO2 max were significantly lower in the players. The AT was larger in the players but the AT/VO2 max was essentially similar to that of the control group. CONCLUSION: Our study reveals that the professonal soccer players, despite their mean ages were approximately 6 years older than the subjects in the control group, had larger VO2 max and VCO2 max, and smaller HR max for their ages. The VE max was similar in both groups. This suggests that the players have higher aerobic capacity than the control group and exchange respiratiory gases more efficiently.