The primary objective of the American Medical Research Expedition to Everest was to obtain information on human physiology at the highest possible altitude, including the Everest summit. An important data point was the barometric pressure on the summit, because this determines the inspired P(O(2)). The first measurement ever taken was 253.0 mmHg. Because modeling studies had shown that extreme hyperventilation was essential to reach these great altitudes, 34 alveolar gas samples were collected above an altitude of 8000 m, including 4 on the summit. These showed that hyperventilation reduced the alveolar P(CO(2)) to between 7 and 8 mmHg in one climber. An important finding was that alveolar P(O(2)) was defended at a value of about 35 mmHg by the increasing hyperventilation as the climbers ascended higher. Venous blood samples collected on two summiters gave a mean base excess of -7.2 meq.L(-1). Using the alveolar P(CO(2)) value, this gave an arterial pH of over 7.7, indicating an extreme degree of respiratory alkalosis. While climbing at an altitude of 8300 m, one summiter showed a respiratory frequency of 86 breaths.min(-1) and tidal volume of 1.26 L, indicating very rapid shallow breathing. Maximal oxygen consumption for the summit was derived by having well-acclimatized subjects exercise maximally at an altitude of 6300 m while breathing 14% oxygen. The V(O(2)) was just over 1 L.min(-1), which is sufficient to explain how exceptional humans can reach the summit without supplementary oxygen. In addition to the measurements at altitudes over 8000 m, data were obtained at two camps at 5400- and 6300-m altitude. These gave information on the control of ventilation, periodic breathing, blood physiology, cerebral function, and metabolism.