In this study, several Hungarian dwellings and working places were surveyed using passive radon- and thoron-measuring devices (Radopot(®) and Raduet(®)) from 2003 to 2008. The detectors were placed 15-30 cm from the wall throughout the 1- to 3-month period. In dwellings, the presence of thoron, ∼100 Bq m(-3), was detected almost in all cases, ; however, in the cellars of these buildings, a value ∼200 Bq m(-3) was typical. In the cases of manganese and bauxite mines, the concentration of thoron was mainly 200 and 500 Bq m(-3), respectively. In caves, it was 1000 Bq m(-3), whereas in the radon bath it was ∼100 Bq m(-3). As in many cases, the ratio between thoron and radon concentrations was >0.25 and the dose contribution from thoron and its progeny was not negligible. Therefore, further investigation on the thoron progeny will be necessary for an accurate dose estimation.