The mutagenic aromatic amines Trp-P-1, Trp-P-2 and Glu-P-1, isolated frm pyrolysates of tryptophan and glutamic acid, at the concentration of 0.025 mM were treated with 0.05 mM nitrite at various pH values at 37 degrees C. The resulting reaction mixtures were tested for mutagenicity towards Salmonella typhimurium TA98 and TA100. When treated with nitrite at this physiologically realistic concentration, these mutagenic aromatic amines were readily converted to extremely weak or non-mutagenic deaminated compounds. These deaminated products were identified as the corresponding hydroxy compounds by mass and proton magnetic resonance spectroscopies. Comparative kinetic studies were made on the disappearance of the mutagenic aromatic amines. The half-life (t1/2 of Glu-P-1 on treatment with nitrite at pH 1.6 was less than 5 min, and those of Trp-P-1 and Trp-P-2 were 95 and 105 min, resp.