The three IQ (2-amino-3-methylimidazo[4,5-f]quinoline) compounds IQ, MeIQx (2-amino-3,4-dimethyl[4,5-f]quinoxaline) and MeIQ (2-amino-3,4-dimethylimidazo[4,5-f]quinoline) have been found in boiled pork juice. To determine which Maillard reaction products are important in the formation of IQ-type mutagens in boiled pork juice, six Maillard reaction products were separately added to the pork juice before reflux boiling and then the mutagenicity of each sample was examined with Salmonella typhimurium TA98 in the presence of S9 mix. The addition of four Maillard reaction products enhanced the mutagenicity of pork juice 1.2-2.9-fold after reflux boiling. The highest level of enhancement was observed with tetrahydrothiophene, followed by 2,3-dimethylpyrazine, 3-methylpyridine and 2-methylpyridine. However, the addition of 2-acetylpyrrole and imidazole greatly inhibited the mutagenicity of pork juice. To confirm which IQ-type mutagens were changed, four major mutagenic fractions were monitored after HPLC separation by their mutagenicity with Salmonella typhimurium TA98. By comparing the retention time of authentic IQ compounds from boiled pork juice with added tetrahydrothiophene or 2,3-dimethylpyrazine, we show that four major HPLC fractions have significantly increased mutagenicity compared with the same fractions in boiled pork juice alone. In contrast, the mutagenicity of these fractions was considerably reduced with the addition of imidazole or 2-acetylpyrrole to the pork juice before refluxing. The residual amounts of tetrahydrothiophene and 2,3-dimethylpyrazine added to the boiled pork juice after heating were measured by gas chromatography and found to be inversely correlated with the mutagenicity of the pork juice.(ABSTRACT TRUNCATED AT 250 WORDS)