This European Standard describes a method for the determination of monomethylmercury (MMHg) in foodstuffs of marine origin. The method has been validated in an interlaboratory test on mussel tissue, squid muscle, crab claw muscle, dog fish liver, whale meat, cod muscle and Greenland halibut muscle (all freeze-dried) with mass fractions from 0,04 mg/kg to 3,6 mg/kg dry weight according to ISO 5725-2 [1]. Laboratory experiences have shown that this method is also applicable on fresh samples [2].