Levels of radioactive caesium (Cs-137) were determined in minke whales (Balaenoptera acutorostrata) from West Greenland, the Northeast Atlantic region and the North Sea. The sample consisted of muscle tissue from 135 minke whales caught in 1998 in 7 different areas: West Greenland, n = 44; East Greenland, n = 4; Jan Mayen, n = 22; Svalbard, n = 14; Barents Sea, n=20; Vestfjorden/Lofoten, n=14; the North Sea, n = 17. Mean Cs-137 levels in whales ranged from 0.298 (SD=0.083) Bq kg(-1) wet weight around Svalbard to 1.319 (SD=0.587) Bq kg(-1) wet weight in the North Sea. The finding of the highest caesium concentration in minke whales from the North Sea is in accordance with previous findings that Cs-137 levels in the marine environment of the North Atlantic region decrease with increasing distance from major point sources (i.e. nuclear-fuel reprocessing plants in the UK and France, and outflow from the Baltic Sea containing Cs-137 from the 1986 Chernobyl accident). The mean Cs-137 levels in minke whales from Svalbard and the North Sea differed significantly from mean levels in the other areas. This difference supports the indications from other studies that groups of minke whales are resident for some time at their feeding grounds in the North Atlantic and may occur in separate stocks during summer.