The composition of fatty acids in selected tissues of two populations of cod and three redfish species was determined by the fatty acid profile method: a chemometric method, consisting of methanolysis, gas chromatography of the resulting fatty acid methyl esters and multivariate statistical treatment of the analytical data. The two reared stocks of cod from the Faroe Bank and the Faroe Plateau had significantly different fatty acid profiles in total lipids and in phosphatidylethanolamine and phosphatidylcholine from heart tissue. This difference is expected to be genetic and free of biotic and abiotic impacts on the fatty acid profiles. The three species of redfish from waters off the Faroe Islands and Norway had significantly different fatty acid profiles in selected tissues. The fatty acid profiles appear to be species specific. The mutual relationship between Sebastes marinus and S. mentella is closer than the relationship between either of them and S. viviparus. Analysis of the fatty acid profile in the heart tissue of S. mentella from eleven locations has revealed a stock-structure, comprising four separate stocks of Sebastes mentella in the North Atlantic.