The purpose of this study is to determine the aerobic capacity in a group of smokers and to carry out a prospective study of the changes in cardiorespiratory and metabolic response to exercise after smoking withdrawal. An aerobic capacity test was performed in 90 smokers and 30 non-smokers. Afterwards, the smokers were included in a smoking withdrawal program. One year later, the aerobic capacity test was repeated in those individuals who were able to stop smoking. The initial study of the aerobic capacity during exercise showed that smokers had significantly lower values of maximal oxygen uptake per kg body weight (VO2 max./kg) (28.7 +/- 8 vs. 35.1 +/- 7 ml/kg/min) (p < 0.001), work time (5.8 +/- 2.6 vs. 7.5 +/- 3.1 min) (p < 0.01) and work load (1.1 +/- 0.3 vs. 1.4 +/- 0.3 W/kg) (p < 0.001) under aerobic conditions. Aerobic capacity test performed one year after smoking withdrawal in those who were able to stop smoking showed a significant increase in VO2 max./kg (35.5 +/- 6.1 vs. 31.1 +/- 5.5) (p < 0.05), work time (8.1 +/- 3.2 vs. 5.8 +/- 3.2 min) (p < 0.05) and work load (1.5 +/- 0.4 vs. 1.1 +/- 0.4 W/kg) (p < 0.01) under aerobic conditions. No differences were observed in the aerobic capacity test performed on the ten subjects who did not stop smoking. From these data we suggest that tobacco consumption produces impairment of the aerobic capacity that can be reverted, at least in part, after smoking withdrawal.