Seven trees were felled in the Briansk region in 1997. The trees were sectioned for sampling, both at different heights and according to year rings, and samples were analysed for content of Cs-137. I, general, the specific activity of Cs-137 was much higher in the fresh parts of the three (needles, leaves and twigs) than in the core wood. The year ring study showed that Cs-137 had penetrated deeply in to the trunk, and no peak was detectable in the year ring corresponding to the Chernobyl accident in 1986. The specific activity in the trunk wood had a maximum at the height corresponding to the growth years at approximately 1986. Neutron activation analysis was used to analyse for stable Cs. The results showed that the relationship between concentrations of Cs-137 and stable caesium is much higher in the newer parts of growing trees than in the older parts. Together with a tendency of inward migration this leads to a preliminary conclusion that the Cs-137 activity will continue to accumulate in the core wood. (C) 2001 Elsevier Science B.V. All rights reserved.