Total arsenic concentrations were determined in three teleost species (herring Clupea harengus; cod Gadus morhua, and flounder Platichthys flesus) taken from four locations in the Baltic and North Sea with salinities ranging from 8 to 32 psu. Individual arsenic concentrations ranged from 0·04 to 10·9 mg/kg wet mass, and there was a positive linear relationship between arsenic concentration and salinity for all three species (r2 0·44 to 0·72, all P<0·001). Although it is well known that marine fish contain much higher concentrations of arsenic than do freshwater fish, the data reported here are the first showing a relationship between the total arsenic concentration in fish and salinity.