N-Nitroso-N-(3-keto-1,2-butanediol)-3'-nitrotyramine (NO-NTA) is a product of a model browning system in the presence of sodium nitrite. In this study, the chemical structure is confirmed by spectral studies, including UV, mass spectrometry, nuclear magnetic resonance and infrared spectroscopy. NO-NTA is strongly genotoxic to the rat hepatocyte and is moderately cytotoxic to mouse C3H10T1/2 cells. Results obtained in this study indicate that NO-NTA inflicted DNA damage through the formation of a DNA adduct. In addition, C3H10T1/2 cells were treated with NO-NTA and, following addition of 12-O-tetradecanoylphorbol-13-acetate (TPA) as promotor, the increase of transformed foci indicated that NO-NTA could possibly be an initiator [corrected] of TPA tumor promotion. A transformed cell line from NO-NTA initiated and TPA promoted foci increased saturation density and growth ability in soft agar reactive to the control line. These results suggest that the formation of a genotoxic agent of nitroso-derivatives may take place in a nitrite-containing food system during processing and cooking.