Radon and thoron are the precursor radioactive gases responsible for natural radiation exposures to general populations. A time integrated measurement method has been developed for estimating their concentrations using nuclear track detector based passive dosimeters. These enable the long term measurements of radon and thoron in dwellings covering diurnal and seasonal variations for estimating annual average inhalation doses to residents. Being a cost effective technique, it is ideally suited for large scale surveysin high back ground radiation areas for estimating population doses for epidemiological studies.