Assessment of the breathing pattern at maximal exercise in patients is limited because the range of ventilatory responses (minute ventilation; tidal volume; respiratory rate) at maximal exercise in normal humans is unknown. We studied 231 normal subjects (120 women; 111 men) equally distributed according to age from 20 to 80 years. Each subject performed a progressive incremental cycle ergometer exercise test to their symptom-limited maximum. Mean ventilation at the end of exercise (Vemax) was significantly higher in men (mean +/- SD, 97 +/- 25 L/min) than in women (69 +/- 22 L/min) (p less than 0.001). Minute ventilation at the end of exercise as a fraction of predicted maximal voluntary ventilation (Vemax/MVV) for all subjects was 0.61 +/- 0.14 (range, 0.28 to 1.02). There was no difference in Vemax/MVV between men (0.62 +/- 0.14) and women (0.59 +/- 0.14). Tidal volume at the end of exercise (Vtmax) was higher in men (2.70 +/- 0.48 L) than in women (1.92 +/- 0.41 L) (p less than 0.001). Any differences in Vtmax between men and women disappeared when Vtmax was corrected for baseline FVC. Respiratory rate at the end of exercise (RRmax) was 36.1 +/- 9.2 breaths per minute for all subjects. There was no difference in RRmax between men and women. The Vemax correlated best with carbon dioxide output at the end of exercise (r = 0.91; p less than 0.001) and with maximal oxygen uptake (r = 0.90; p less than 0.001) for all subjects. This study of a large group of subjects has demonstrated the wide range of possible breathing patterns which are adopted during exercise and has provided a wide range of "normal" responses which must be taken into consideration when maximal ventilatory data from exercise tests are analyzed.