Dyspnea, anorexia, insomnia, and headaches are frequent symptoms in visitors to the South Pole. Intense cold, low humidity, altitude, and isolation are the major stresses. This study was undertaken to explore the mechanisms of symptoms and the physiological changes in man after arrival at the pole and during the course of one year there. Arterial hypoxia, hyperventilation, and erythrocytosis occurred as anticipated in the high-altitude environment. Exposure to intense cold resulted in little evidence of airway obstruction. Carboxyhemoglobin was present in significant amounts, even in nonsmokers, and may be related to inadequate ventilation of the underground living quarters. These factors and their relationship to isolation, dietary restriction, the sixmonth day-night cycle, and other stresses may be important in the production of symptoms at the pole.