Mutagenicity of oil of charred egg yolk (called ranyu in Japanese), which is commercially available and consumed as a health food in Japan, was tested on Salmonella typhimurium strains TA98 and TA100 with and without metabolic activation. Both strains showed a high response to the oil, and the number of His+ revertant colonies with strain TA98 was 15,000-20,000 for 1 g equivalent amount of oil. The mutagens were purified by acid extraction, chloroform extraction after alkalization, dialysis, adsorption to blue cotton, passing through a Sephadex LH-20 column and several stages of high-pressure liquid chromatography with reverse-phase columns. At least 7 heterocyclic amine mutagens were detected. Two of them were suggested to be 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-6-methyldipyrido [1,2-a:3',2'-d]imidazole (Glu-P-1). One was suggested to be 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ). The others were not identified but distinguishable from 12 known heterocyclic amine mutagens. The estimated minimum contents of IQ and Glu-P-1 were 1.1 ng/g and 4.8 ng/g, respectively.