Abstract Concentrations of 103Ru, 131I, 134Cs and 137Cs deposited in the fallout from the Chernobyl reactor accident in the environs of Bonn (FRG) and of the natural radionuclide 40K were measured in soils, food crops, milk and pasture vegetation between May 1986 and September 1987. Soil-to-plant concentration factors and transfer coefficients from feed to milk were determined. Geometric means for the soil-to-plant concentration factors for 40K and 137Cs into pasture vegetation were obtained as B v = 0·54 and 4·2 × 10 −2, respectively. The geometric means for the soil-to-plant concentration factors for 134Cs, 137Cs and 40K for field-grown food crops were found to be 9·0 × 10 −2, 2·5 × 10 −2 and 0·17, respectively. For the 1986 and 1987 grazing seasons, the transfer coefficients for 134Cs, 137Cs and 40K from feed to milk, F M, could be determined. The F M values (geometric means) obtained were: for 134Cs, 3·7 × 10 −3 (d/litre) and, for 40K, 2·2 × 10 −3 (d/litre). For the 1986 grazing season, and F M value of 4·2 × 10 −3 (d/litre) for 131I could also be measured. Concentration-depth profiles of 137Cs have been measured in soil cores at two sites, a permanent pasture and an undisturbed area without vegetation. Using a diffusion-like model for the transport of 137Cs in the soil core, a root mean square displacement of x ≅ 2 cm could be derived for the 3 year period following the Chernobyl accident. Resultant whole body doses from consumption of food containing 134Cs and 137Cs and produced at locations in the environs of Bonn were estimated at 14·7 μSv for 1986 and 0·56 μSv for 1987.