The geochemical characteristics of the hot spring waters in the Rehai and Ruidian geothermal fields, Tengchong County, Yunnan Province, China are described and their possible environmental impact assessed. The results show that the alkaline spring waters contain high levels of K, Na, F, Cl, SiO2, whereas the only acidic sprim, water in Rellai geothermal field contains high levels of SO42-, Mn and Fe. As and Sb in the spring Waters are in the range 43.6-687 mu g/L and 0.38-23.8 mu g/L, respectively. As(III) occurs in most spring waters. and constitutes up to 91 % of the total As. A fraction of the geothermal As and Sb is trapped in the sinter deposits while most enters the environment. The diffusion of As and Sh into groundwater and downstream crop fields constitutes I threat to the health of the local population. (C) 2007 Elsevier Ltd. All rights reserved.