We have studied the activity of the weak endogenous oxidant N-chlorotaurine against Mycobacterium terrae. The study revealed slow killing of more than 2h duration by 1% (55 mM) N-chlorotaurine. In the presence of ammonium chloride, however, killing times decreased to a few minutes, even by 0.1% N-chlorotaurine. This phenomenon is explained by formation of the lipophilic and therefore more bactericidal monochloramine as a result of transhalogenation of ammonia by N-chlorotaurine.