Nitrite was consistently found in human saliva at levels of usually 6-10 ppm. The nitrite level did not seem to be strongly influenced by the composition of a meal, and in some individuals a narrow range of nitrite concentration was maintained for a long time. In agreement with earlier work, parotid ductal saliva was found to be free of nitrite, and a major route of nitrite formation was via microbial reduction of nitrate naturally present in saliva. Exploration of various parameters related to the reduction of nitrate to nitrite did not demonstrate a clear correlation between measurements on individuals and their level of salivary nitrite. The microorganisms responsible for nitrite formation were identified and quantified, and the relationships between nitrate consumption and nitrite formation explored. These complex relationships suggested that the tree nitrite in saliva represents the “spillover” of that formed in microbial cells.