BACKGROUND:In non-small-cell lung cancer patients, high peak oxygen uptake (peak V O 2 ) predicts lower rates of postoperative complications and better long-term survival. Neoadjuvant chemotherapy (NAC) may negatively impact peak V O 2 . METHODS: Cardiopulmonary exercise testing (CPET) was performed in 34 consecutive stage IIIA/IIIB non-small-cell lung cancer subjects scheduled for elective lung surgery. Using multivariate linear regression adjusted for potential confounders, we compared CPET results in subjects receiving or not receiving NAC (NAC؉, n ؍ 19; NAC؊, n ؍ 15). RESULTS: Adjusted peak V O 2 was lower in NAC ؉ compared with NAC؊ subjects (؊5.3 mL/min/kg [95% CI ؊8.3 to ؊2.2], P ؍ .01). Likewise, oxygen pulse, maximal work load, and ventilatory threshold were also lower in NAC؉ subjects, whereas peak heart rate and breathing reserve were similar. NAC؉ subjects presented lower values of diffusion capacity for carbon monoxide (D LCO ) (P ؍ .035) and hemoglobin concentrations (P < .001). D LCO was strongly correlated with peak V O 2 (r 2 ؍ 0.56). Adjustment for D LCO reduced the effect of NAC on peak V O 2 without suppressing it. CONCLUSIONS: NAC was associated with lower preoperative peak V O 2 in subjects with non-small-cell lung cancer. This lower aerobic fitness may result from NAC-induced reduction in pulmonary gas exchange or heart toxicity. Since lower fitness is linked to poorer outcome, the decision for NAC may have to be balanced with its possible toxicity.