The alkylating activity of extracts from several fish products with or without sodium nitrite in simulated gastric juice has been investigated. Some of the extracts had strong alkylating potency which may be due to the action of the formed N-nitrosamides. These compounds were not derived from nitrosation of methylguanidine and agmatine or from pyrolysis products of the processed fish. The results suggest an urgent need for a comprehensive investigation of nitrosation of various foods in simulated gastric juice.