The aero-cycling posture has become increasingly popular among cyclists. Because of the potential for altered lung mechanics in the aero-cycling posture, the ventilatory and gas exchange profiles of 10 moderately trained males (31.1 +/- 6.3 yr, mean +/- SD) exercising on a cycle ergometer in the upright posture (UC) and aero-cycling (AC) posture were studied. Exercise consisted of 3-min work stages with 50-W incremental changes until volitional exhaustion. Ventilatory and gas exchange responses to exercise were averaged each minute. Maximal oxygen consumption (54.3 +/- 6.3 vs 53.4 +/- 6.9 ml.kg-1.min-1) in the UC and AC were not significantly different. Maximal values for ventilation (132.5 +/- 32.3 vs 128.0 +/- 28.7 l.min-1), tidal volume (2.7 +/- 0.5 vs 2.6 +/- 0.3 1.br-1), breathing frequency (50.0 +/- 8.0 vs 47.0 +/- 5.0 br.min-1), and submaximal ventilatory and heart rate responses in the UC were not significantly different compared with the AC. No significant difference existed between postures for mean inspiratory flow and inspiratory duty cycle at comparable submaximal power outputs. These results indicate that at absolute power outputs, ventilatory responses, as determined by respiratory pattern and timing, and metabolic cost, were similar in the UC and AC. Thus, the AC does not impair physiologic responses to high intensity exercise.