Abstract Accumulations of the radionuclides 137Cs, 134Cs, 106Ru, 103Ru and 110m Ag in seaweed and molluscs have been studied in the months following Chernobyl. The data set ptovides information on the performance of marine organisms as bioindicators for monitoring radioactive contamination. Concentrations of Cs, Ru and Ag radionuclides in Fucus vesiculosus declined with biological half-lives of 57, 80 and 210 days respectively. The biological half-lives of Cs and Ru radioisotopes in Patella were about 40 and 180 days but the decline in levels of 110mAg was less than would have been expected from radioactive decay. Concentrations of 110mAg in marine organisms on the north and east coast have been much higher than those on the west possibly due to differences in enhancement by runoff from nearby land. Radionuclide levels in sea spume were several thousand times greater than in seawater in June 1986.