The implementation of the nuclear programme in the Cheliabinsk region in the Ural, where plutonium for the first Soviet nuclear weapons was produced, involved radioactive contamination of the environment. The end of the cold war in the late 1980s initiated a fruitful co-operation between Russian and Western radioecologists. The present study is a joint Russian-Ukrainian-Danish effort to make an independent estimate of the inventories of Sr-90, Cs-137 and Pu-239,Pu-240 from two major contamination events in the South Urals, namely, the Kyshtym accident in 1957 and the Karachay wind dispersion in 1967. The calculations are based upon deposition measurements of the radionuclides carried out on soil samples assuming that the depositions decreased exponentially with distance from the two sources. The inventory estimates are compared with the available Russian information on the two accidents. (C) 1997 Elsevier Science B.V.