ABSTRACT
The concentrations of radon-222 in the air of some buildings in Olsztyn were measured. The main source of radon in buildings is in general the ground under building and the materials used for building structure. In this work the results of radon-222 concentration measurements in the air of some buildings constructed before the 1939 year, in the buildings constructed after 1945 year with the traditional use of the bricks and in the buildings constructed with the use of great prefabricated plates are presented. The relations between radon-222 concentrations in the basements and in the first floor flats situated above the basement were evaluated. Based on the mean radon concentrations in the air of the various types of buildings investigated the effective doses for the inhabitants of each type of buildings were estimated.