Jáchymov is known as a spa using in balneological procedures among others the radon content of the subsoil. The therapeutic effects of Jáchymov radon waters are used since 1906. In the locality a high natural ionization of the atmosphere can be anticipated which hastens the sedimentation of flying dust aerosol and thus purifies the atmosphere. A stay in a permanently purified and ionized atmosphere has a favourable impact on the health of exposed subjects. The authors made assessment of the electroionic microclimate at selected places of three major spa facilities. The measurements were made at the sites of the most frequent stay of patients and staff. Part of the measurements was evaluation of the environmental concentration of light ions of both polarities. A high ionization of the atmosphere was found indoors as well as outdoors. The values inside the premises reach concentrations of n.10 3 for light ions of both polarities. Although they are recommended as the long-term optimum for humans, they are only exceptional in the Czech Republic due to the contamination of the atmosphere. Evaluation of the patients health status confirmed the favourable effect of the highly ionized atmosphere.

        Key words: ions, spa, climatic treatment, Jáchymov