[en] The ¹³⁷Cs concentration in reindeer meat varies throughout the year due to changes in food selection. During summer, the reindeer eat herbaceous vegetation, and in the autumn large amounts of mushrooms - if available. In winter they prefer to eat ground and arboreal lichen, and these have a much higher radiocaesium concentration than the vegetation eaten during summer. The increase in the reindeer stock in Finland as well as in Norway and Sweden, has lead to overgrazing and degradation of the lichen ranges. The range of winter fodder available for reindeer today is not the same as that in the 60's and 70's following the nuclear weapons fallout period and the previously used ecological half-life values may no longer be applicable to the present situation. After the accident at Chernobyl in 1986 an extensive program was started to monitor ¹³⁷Cs concentrations in the reindeer meat produced in Finland. At the present time the program, which is carried out every 5th year, covers the whole of the Finnish reindeer herding area, i.e. 56 co-operatives. In addition STUK annually measures samples from the 11 northernmost Sami reindeer herding co-operatives as well as from 3 co-operatives close to the Russian border. In this paper the decrease in the ¹³⁷Cs concentration in reindeer meat in three co-operatives, Paistunturi, Ivalo and Kemin Sompio, are presented and ecological half-lives estimated. (orig.)