Keshan disease in China is distributed in a transitional area between the humid region in the south-eastern part and the semiarid and arid regions in the north-western part. It forms a wide belt running from the North-East to the South-West, known as disease zone. Both sides beyond the zone are disease-free. They are respectively called the south-eastern non-disease and the north- western non-disease zones. The districts of Keshan disease distributed uncontinuously as patches.The disease zone presents a low selenium environment where the soil-plant-animal-man system is in a circulation of low selenium. The inhabitants there are mainly fed on local agricultural and supplementary foods. The constitution of their diet is quite simple and poor, lacking entirely of sea products. The fact causing Keshan disease in some particular districts is the biological effect of low selenium environment. The con-tent of selenium in human hair presenting at random on 2129 samples of persons at 181 points in 17 provinces, cities and autonomous regions indicates that it increases re-gularly from the disease zone to the disease-free ones.According to the difference in physical environment and the geographical location of disease districts, the disease zone might be divided into three major regions: the North-Eastern region, the North-Western region and the South-Western (including Tibet) region. The mean value of selenium content in human hair in the North-Bastern region is 0.069±0.027 ppm, in the North-Western and the South-Western regions 0.093±0.032 ppm and 0.087±0.032 ppm respectively. The differences are not remarkable (p＞0.05). The total mean value is 0.085±0.032ppm. Yet. in these three regions mentioned above, the mean values of selenium content in human hair for the disease-free districts adjacent to the disease districts are 0.146±0.032 ppm, 0.209±0.108 ppm and 0.17±0.057 ppm respectively. The total mean value is 0.187ii:0.086 ppm. The differences between disease and disease-free districts within the disease zone are exceptionally remarkable (p ＜ 0.001).Tibet is an unique physico-geographical region. The disease districts are distri-buted in the semiarid temperate montane shrub and alpine steppe belts in south Tibet where the selenium content in human hair is 0.067±0.036 ppm. The semi-humid cold-temperate alpine shrub-steppe belt in North Tibet is disease-freeregion. And the semi-humid warm-temperate montane coniferous forest belt in East Tibet is the district of Kaschin-Beck’s-disease, where the selenium content in human hair is 0.256±0.045 ppm or 0.076±0.039 ppm, the same as that in other districts.The results mentioned above show that there is no remarkable change of selenium content in human hair for any disease districts that are distributed in different regions and inhabited by different nationalities. Obviously, the low selenium environment se-rves as a physico-geographical index.The south-eastern non-disease zone differs greatly from the disease zone in physi-cal environment. The selenium content in human hair in the subtropical yellow-brownish and yellow-cinnamon soils zone (IVA₁) is basically correspondent with that in the red and yellow earths zone (IVA₂), being 0.383±0.130 ppm and 0.333± 0.079 ppm respec-tively. The selenium content in human hair in the lateritic red earth zone (IVAs) is identical with that in latosol zone (in its western part VA₁) and the mean value is 0.493±0.062 ppm, and 0.491±0.085 ppm. For the north-western non-disease zone, the content of selenium is close to that in the south-eastern non-disease zone. Within them the mean value in the temperate piedmont desert-steppe with sierozen zone (in its eastern part, HD₂) is 0.462±0.122 ppm. It is consistent with that in IVA₃ and VA, zones within the south-eastern non-disease zone. They are 0.391±0.135 and 0.366?.109 ppm in warmtemperate grey-brownish desert soil zone (HD₃) and brown desert soil zone (HID₁). In forest-steppe and meadow-steppe zone (VHC₁) on Tibetan plateau it is 0.240 ±0.045 ppm.The frequency distribution cur