Radon(Rn) contents in the air of radioactive spring areas were determined using an ionization chamber equipped with vibrating reed electrometer. The results were as follows: (1) Rn contents in the outdoor air at spa areas of Misasa. Sekigane and Togoo were 0.7 ± 0.4 pCi/l. 0.6±0.3pCi/l and 0.5±0.2 pCi/l respectively. Rn contents in the air both at Misasa and at Sekigane were significantly higher than at none spa area of Kurayoshi city (0.3±0.2pCi/l). (2) Rn contents in the outdoor air at Misasa spa tend to increase from June to September in the year. (3) In usual rooms where spring water is not used. Rn contens in the air were below 1.0 pCi/l. Rn contents in the air of facilities using spring water were determined; peloid therapy room:
2.0±0.4 pCi/l, usual bath rooms: 6.3±1.3 pCi/l (before the bathing). 21.8±2.1 pCi/l (immediately after bathing), Hubbard bath room: 6.7±0.3 pCi/l (before the bubbling), 143.4±69.8 pCi/l (during the bubbling), exercise pool room : 4.3±0.3 pCi/l (before the exercise). 7.4 ± 0.8 pCi/l (during the exercise) and drinking hall: 30.0～47.0 pCi/l respectively.