Physiological reactions to the cold of 29 wintering members of the 9th Japanese Antaractic Research Expedition (1968-1969) were studied at Syowa Station, Antarctica, and during the South Pole Traverse. The members were divided into two groups ; the traverse members whose main project was the South Pole Traverse, and the base members who were engaged in observation activities at the station. Mean outside temperature was -10℃ (+9.5℃ to -32.4℃), mean wind velocity was 6.4 m/s and mean humidity was 62% at Syowa Station during the wintering. 1. Lying and sitting occupied approximately 60% of the time of a day. About 30% of the time by the traverse members at the station, and 12-13% of the time by the base members and by the traverse members during the traverse, were spent in various outdoor activities. 2. As to the average 24-hour energy expenditure, a large amount of energy was expended in such activities as sleeping, observation and light work at the station, and in sitting and driving during the traverse. 3. Energy balance was positive at the station and negative during the traverse. 4. Basal metabolism showed seasonal variation. It increased when the outside temperature lowered, and decreased as the outside temperature rose. This is considered to be the result of acclimatization to the cold. 5. Body weight tended to increase at the station, and this is considered to be caused by the positive energy balance. A significant positive correlation was found between the skinfold thickness of the abdomen and the body weight. 6. Arterial blood pressure tended to fall in winter and to rise during the traverse. 7. After the autumn traverse concentration of blood was recognized. During the South Pole Traverse with the well-equipped snow vehicles, concentration of blood was hardly observed, but erythrocytosis due to the high altitude and unexplained leukopenia were noticed. Relative increase of lymohocyte in percentage of differential leukocyte count was also recorded during the South Pole Taverse. 8. The vital capacity of lung tended to decrease due to physical fatigue.