AbstractThe thermal properties of atmospheric air surrounding the human body at various altitudes are characterized with a system of parameters. This system comprises resistance of the air to convective heat transfer hc1, C (W/m2)1 and to water vapour transfer hD1, s/m. The concept of evaporative resistancehe1, hPa (W/m2)1) following the similarity of the processes is introduced. In obtaining the altitude dependencies of investigated paramters, a respective heat transfer equation expressing the rate of heat exchange at the boundary body surface ambient air is applied. The use of the body thermal state of the established altitude dependencies is discussed. The concept of thermal stability related to the evaporative resistance parameter he1 is introduced. This parameter is assumed as: (1) an indicator of the human body thermal stability and (2) distributor and predictor of environmental influence on the body thermal state.