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The cold tolerance of 11 Japanese and 9 Caucasian residents of Hawaii who had not been recently exposed to cold were compared. Three-hour cold water and three-hour cold air exposures were employed. Tissue insula­tion and critical temperatures were computed on the basis of surface and rectal temperatures and oxygen uptake. Critical temperatures in air averaged 23.2°C for Japanese and 24.3°C for Caucasians, and in water the values were 31.5°C and 30.9°C respectively. These are not statistically different. The Japanese had higher maximal insulation, but the differences were not significant when the effects of subcutaneous fat were removed. It is argued that subcutaneous fat is more important than inherited physiological differ­ences in conditioning response to cold for these subjects.