Purpose The aim of the present study was to evaluate the determinants of gas exchange in smoking and nonsmoking teenagers during an incremental exercise test. Materials and Methods One hundred and fifty healthy Bulgarian school children in the age span 15 -17 years took part in the study. All participants completed anthropometric measurementsstanding height, weight and BMI and a questionnaire about smoking habits. The studied group performed an incremental exercise test on a treadmill following a modified Balke protocol. Results Near 90% of participating teenagers completed the exercise test to the end. Boys showed significantly higher values of oxygen consumption on different levels of the test and maximal oxygen consumption -VO 2 peak mL.min-1 = 2287 ±337 vs. 1702±278; p<0.001. In the studied population, smokers had slightly lower values without a significant difference -VO 2 peak mL.min-1 = 1777±288 vs. 1851±417; NS. VO 2 increases with age and correlated best with weight (R=0.83) and height (R=0.65) but less with BMI (R=0.59). Ventilatory equivalents for O 2 and CO 2 (V E /VO 2 , V E /VCO 2 ) decline with age. Girls in comparison with the boys had greater fatigue perception (Borg scale) during the incremental test.Conclusions The anthropometric parameters were the best determinants of physical capacity in teenagers. Smokers showed slightly lower but not significant values for VO 2 peak. Boys had significantly higher values for VO 2 peak compared with girls.