[en] In the context of radiation protection for both workers and the population in general, natural sources of radiation, and in particular radon gas and its short-life decay products assume great importance. In particular, workers in thermal spas can easily be exposed to a level of radon radiation and its decay products comparable to those in uranium mines, though often these workers are unaware of the danger. The main source of radon in thermal baths is the thermal water itself, coming as it often does from deep springs, and this can produce high radon concentrations which are left in those areas in which therapy is carried out. Another factor which cannot be overlooked is the radioactive content of thermal mud, often matured for long periods by contact with thermal water. Thermal cures, though varying slightly from site to site, consist principally of mud cures, hydro-therapy and inhalation in various forms. Both health workers and patients are exposed to radiation, most importantly certainly through inhalation, though in certain procedures ingestion and irradiation are also important factors. International organizations have been addressing the problem of radiation exposure to health workers in spas for a number of years and recently protective legislation has been introduced regarding the use of natural springs. In 1996, Directive 96/29/EURATOM, was issued which reflects the norms advocated in ICRP publications, notably publication no.65. This directive was subsequently embodied in Italian legislation (DL 241/00), providing for precise quantification of exposure levels for health spa workers. The object of the project undertaken by our group was thus the evaluation of the radiation doses for health workers and their patients in an Italian thermal health centre. A necessary step towards this was the exact measurement of radon concentrations in places where workers and patients are to be found