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Radon and thoron exhalation rates and gamma-ray dose rate in different places in Hiroshima Prefecture were measured. Exhalation rates were measured using an accumulation chamber method. The radon exhalation rate was found to vary from 3 to 37 mBq m−2 s−1, while the thoron exhalation rate ranged from 40 to 3330 mBq m−2 s−1. The highest radon exhalation rate (37 mBq m−2 s−1) and gamma-ray dose rate (92 nGy h−1) were found in the same city (Kure City). In Kure City, indoor radon and thoron concentrations were previously measured at nine selected houses using a radon–thoron discriminative detector (Raduet). The indoor radon concentrations varied from 16 to 78 Bq m−3, which was higher than the average value in Japan (15.5 Bq m−3). The indoor thoron concentration ranged from ND (not detected: below a detection limit of approximately 10 Bq m−3) to 314 Bq m−3. The results suggest that radon exhalation rate from the ground is an influential factor for indoor radon concentration. [ABSTRACT FROM AUTHOR]