The importance of using masks during exercise has increased since the coronavirus disease-2019 (COVID-19). This study aimed to investigate the effects of using surgical masks on gas exchange and exercise responses in maximal exercise. Twenty-six participants were included. Participants performed the maximal exercise tests twice, masked, and unmasked. Gas exchange parameters (at maximal exercise and anaerobic threshold [AT]) and hemodynamic responses were measured. In the hemodynamic responses measured at rest, only the saturation of peripheral oxygen (SpO(2)) was lower in the masked (mean: 97.23 +/- 1.33%) measurement than in the unmasked (mean: 97.96 +/- 1.07%) measurement (p = 0.006). Test duration was lower in the masked test (unmasked: 10.32 +/- 1.36 min vs. masked: 10.03 +/- 1.42 min, p = 0.030). Peak oxygen consumption (VO2peak) (unmasked: 31.23 +/- 5.37 vs. masked: 27.03 +/- 6.46 ml/kg/min), minute ventilation (V-E) l/min, and energy expenditure (EE) kcal/hour were higher in unmasked tests (p < 0.001). There was no difference in the gas exchange parameters measured at the AT in the masked and unmasked tests (p > 0.05). Respiratory gas exchange parameters were affected in peak exercise due to increased respiratory workload, but not at the AT. There was no change in hemodynamic responses because vascular control may not be affected by mask usage.