CI Solvent Yellow 14 has been reported to be carcinogenic in the rat, inducing neoplastic liver nodules, but non-carcinogenic in the mouse. The present experiments have extended previously reported investigations on the activity of CI Solvent Yellow 14 in in vivo genotoxicity assays. CI Solvent Yellow 14 has been examined for genotoxicity in vivo in the bone marrow micronucleus assay in both the rat and the mouse, and in the rat liver unscheduled DNA synthesis (DNA repair) assay, to limit doses of 5000 and 2000 mg/kg respectively, by oral gavage. CI Solvent Yellow 14 showed evidence of clastogenic activity in both the rat and mouse bone marrow (clear effect in the rat; weak effect in the mouse), but no evidence of DNA repair in the rat liver. In view of the latter finding, the contribution, if any, of the genotoxicity expressed by the micronucleus assay to the formation of liver nodules on chronic administration of the compound, is unclear.