N-Nitroso-N-methylurea (NMU) is a highly potent direct-acting carcinogen that has been shown to induce cancer in a number of animal species. Although previous research has indicated that nitrosation of creatinine (CRN), a common constituent of meats, dried fish, and seafoods, can form traces of NMU, there is uncertainty as to (1) the yield of NMU and (2) whether detectable amounts of NMU can be formed from cured meats following nitrosation under acidic conditions given the low residual levels of nitrite found in cured meats at the present time. Lack of sensitive and specific analytical methods most likely has hindered progress in research in these areas. An HPLC postcolumn denitrosation-thermal energy analyzer technique and a GC-MS confirmation technique were developed for the determination of NMU in cured meats. Both techniques are highly sensitive (0.5 and 0.03 ppb, respectively) and specific. The optimum pH for NMU formation from CRN ranged between pH 1 and pH 3, and the yields of NMU under variable reactant concentrations ranged between 0.00004 and 0.0046%. When 27 samples of various cured meats (10 g aliquots each) were acidified with HCl (final pH values of 0.8-2.5) and incubated at room temperature for 2 h, without any additional nitrite, 24 gave results below detectable levels but 3 formed 2-26 ng of NMU/10 g of meat. Incubation of the negative meats with additional nitrite (50-500 microg/g of meat) formed 0.6-176 ng of NMU/10 g of sample. Although the amounts of NMU formed were extremely small, this seems to be the first reported formation of NMU from cured meats with and without additional nitrite.