N-Chlorotaurine, the main representative of long-lived oxidants found in the supernatant of stimulated granulocytes, has been investigated systematically with regard to its antibacterial activity at different physiological concentrations for the first time. N-Chlorotaurine (12.5 to 50 microM) demonstrated a bactericidal effect i.e., a 2 to 4 log(10) reduction in viable counts, after incubation at 37 degrees C for 6 to 9 h at pH 7.0, which effect was significantly enhanced in an acidic milieu (at pH 5. 0), with a 3 to 4 log(10) reduction after 2 to 3 h. Moreover, bacteria were attenuated after being incubated in N-chlorotaurine for a sublethal time, as demonstrated with the mouse peritonitis model. The supernatant of stimulated granulocytes exhibited similar activity. Transmission electron microscopy revealed changes in the bacterial cell membrane and cytoplasmic disintegration with both reacting systems, even in the case of a mere attenuation. The results of this study suggest a significant bactericidal function of N-chlorotaurine and other chloramines during inflammation.