[en] A brief description was given on the highly radioactive springs in the world. As the typical examples, Badgastein in Austria and Misasa in Japan are explained as follows. Mean radon-222 contents in the atmosphere of the central parts at Badgastein, and Misasa spas were 96.2, 25.9 mBq/l, respectively. mean Rn-222 contents of the thermal waters were 1480 Bq/l in the former and 437 Bq/l in the latter. It was estimated that amounts of Rn-222 emitted from the thermal waters into the atmosphere were 7.4 x 10⁹ at Badgastein spa and 1.3 x 10⁹ (Bq/day) at Misasa spa. The WLM values owing to radon-222 and its daughters on the residents of Misasa spa were rather low. For instance, WLM values of the author's daily life was about 0.021 and of bathing in radioactive springs was 7.0 x 10^-4, respectively. Many residents in Misasa spa were descended from about 800 years ago. There were no significant effects of radioactive bathing and environment on the incidences of infertility, malformation and shortening of lifespan of the residents in the area of Misasa spa. Further, the ratio of the number of deaths by cancer against the total number of deaths was low in Misasa when compared with that of the neighboring villages. (author)