The emission of low temperature, carbon dioxide rich gases from soils, which are related to post-volcanic activity and the dry carbon dioxide spas established on them, are also called mofettes. The phenomenon is really common in the Pannonian Basin, especially in Transylvania, but examples from Hungary are also well known, especially in the case of Mátraderecske and Parádfürdő. In the frame of this research work the occurrence, spatial and temporal changes of radon gas have to be measured in natural mofettes and carbon dioxide baths built for therapeutic purposes, and the reasons of the changes should be interpreted. Another task is to model the subsurface flow of mofette gases in Visual Modflow and COMSOL Multiphysics using existing and new measurement data. The development and application of a personal radon dosimetry method to estimate the radon exposure of personnel serving in carbon dioxide baths is also part of the research.