Due to southeasterly wind and rainfall during the critical days after the Chernobyl accident, Norway got a substantial part of the cesium isotopes released. The radioactive fallout followed closely the rainfall and was mainly concentrated to some thin populated areas in the central parts of the country. This report summerize the results from a post-Chernobyl research program on aquatic and terrestrial ecosystems in contaminated areas. Pathways, processes and factors determining the Cs-137 concentration in soil, plant, water, fish and wild animal were investigated. 84 refs., 40 figs., 20 tabs.