Nitrite inhibited the killing of Escherichia coli by hypochlorous acid. The protection curve was sigmoid. Complete protection occurred at nitrite concentrations greater than that of hypochlorous acid. Hypochlorous acid reacts rapidly with nitrite, as shown by phenolic nitration, using 4-hydroxyphenylacetic acid. The nitration was biphasic. Amines and amino acids inhibited the nitration, but metal chelators and hydroxyl radical scavengers except for dimethylsulfoxide did not. The reaction between hypochlorous acid and nitrite yields nitrating species such as nitrogen dioxide or nitronium ion. Nitrite could protect E. coli by removing toxic nitrating species by hypochlorous acid.