The radon concentration in the air and water of the Bizovac spa was measured by the Radhome silicon detector and the average values were obtained as 70 Bq/m(3) in the indoor pool, 40 Bq/m(3) in the hotel room, 135 Bq/m(3) in the closed therapeutic bathroom, but the geothermal water had a Rn concentration of 25.3 kBq/m(3) and the potable one 2.7 kBq/m(3). The Rn transfer factor (f) from water to air in the indoor pool and therapeutic bathroom was 10 and 40 times higher than for normal dwellings (f(n) = 10(-4)), respectively. The effective equivalent dose of inhaled radon for permanent personnel under the worst conditions in the spa was 5.4 mSv/y, but visitors spending two weeks in the spa could receive the dose of 77 mu Sv. [References: 6]