Because of the genotoxic effects shown by Dimethophrine (DMP) nitrosation mixtures, the interaction between DMP hydrochloride and sodium nitrite in acidic aqueous solution at 37 degrees was investigated in a wide range of reagent concentrations and molar ratios, reaction times and pH values. Actually, depending on the operating conditions, it was possible to detect variable amounts of 2,6-dimethoxy-1,4-benzoquinone (DMBQ), a highly genotoxic compound, but no N-nitrosoderivative. The highest conversion of DMP into DMBQ was obtained when concentrated acidic solutions of DMP and NaNO2 (molar ratio 1:1.9) reacted at pH 3.0-4.0 (50-60% after 1 hour, depending on the pH conditions). When DMP hydrochloride and NaNO2 (molar ratio 1:0.95) were allowed to react at pH 3.5 in a more diluted solution, to mimic gastric conditions, the conversion of DMP into DMBQ after 20 min was about 3%. The breakdown of DMP can be prevented by adding suitable amounts of ascorbic acid to the reagents.