AbstractThe nuclear accident at Chernobyl in April 1986 resulted in a significant increase in the inventory of radiocaesium retained in the soil in many regions of the United Kingdom. The deposition of134Cs provides a convenient tool for the examination of erosional processes in upland systems. Detailed soil sampling has been undertaken within the Plynlimon experimental catchments to establish the pattern of deposition of Chernobyl‐derived radionuclides. The preliminary results of a combined radiometric and mineral magnetic approach to the study of the transport of Chernobyl‐labelled sediments and their source areas on these upland catchments in mid‐Wales are desc