AbstractWithin an EU‐funded research project, 281 textile dye products in use at nine textile finishing companies from eight European countries were assessed for potential mutagenic properties. Most of the dyes belonged to the so‐called existing substances. Data sources considered were data published in the literature, unpublished industrial data provided by dye producing companies, and laboratory testing. Data on mutagenicity are virtually absent for many of the dyes. Unpublished test results performed on behalf of the dye manufacturing industry proved to be an important data source that is not accessible under usual circumstances. Four dye stuffs contained in seven dye products in use at the textile finishing companies were judged to be mutagenic, based on published data from the literature. Mutagenicity testing using Salmonella typhimurium, strains TA98 and TA100, revealed positive results for about 28% (15 out of 53) of the dye products investigated. Upon further testing with the mouse lymphoma assay (L5178Y/TK+/‐) 67% (6 out of 9) of Ames‐positive dyes proved to be mutagenic in this mammalian cell test. All data sources combined led to an overall assessment of 14 dye products out of 281 being mutagenic. For 16 there is a suspicion of mutagenicity due to positive responses in one test but 71 of the dye products are without any data on mutagenicity. This paper describes the data aggregation process, evaluation criteria and the overall assessment, and exemplifies controversial evaluations. Copyright © 2004 John Wiley & Sons, Ltd.