The International Biological Program (IBP) is the successor in the biological field to the International Geophysical Year in the physical field. This report discusses one of the methods, approved by a Working Party of the IBP, for determining the cold tolerance of various ethnic groups under field conditions. A standardized cold stress for an eight-hour period during the night is provided by a portable environmental chamber developed by the contractor. Measurements of metabolism and body temperature, with a high degree of accuracy, and the obtaining of EEG and EMG tracings during the cold exposure, are necessary. These parameters can be obtained by either modifying standard medical laboratory equipment available from commercial sources, or constructing new equipment according to the instructions of the contractor.