Effect of exogenous taurine on HOCl, NH2Cl and other oxidants-induced degradation of hyaluronic acid was investigated. The scavenging action of taurine on HOCl, NH2Cl and other oxidants was examined. The antioxidant action of taurine was also compared with that of thiol compounds. Viscosity of hyaluronic acid was markedly decreased by HOCl and NH2Cl on a dose dependent fashion. The degradative effect of HOCl on hyaluronic acid was greater than that of NH2Cl. Taurine effectively inhibited HOCl-and NH2Cl-induced degradation of hyaluronic acid in a dose dependent fashion. The degradative effect of HOCl was markedly inhibited by DMSO. Fe2+ plus H2O2-induced degradation of hyaluronic acid was inhibited by catalase and DMSO but not affected by taurine. The desradative action of xanthine and xanthine oxidase was effectively inhibited by SOD and catalase but not affected by taurine. HOCl was significantly decomposed by taurine, DMSO, GSH and MPG. Both absorbance of HOCl at 250 nm and absorbance of NH2Cl at 242 nm were significantly increased by the addition of taurine. Interaction of NH2Cl with GSH or MPG showed an initial peak absorbance, but these absorbances were gradually decreased with time. OH production in the presence of Fe2+ and H2O2 was inhibited by catalase and DMSO but not affected by taurine. Taurine did not affect 1O2 production by U.V. irradiation which is responsible for DABCO and DABA. GSH and MPG markedly inhibited the degradative action of HOCl. These results suggest that the protective action of taurine on oxidants-induced damages of tissue components, including degradation of hyaluronic acid may be attributable to both its scavenging action on HOCl and NH2Cl and the complex formation of taurine with HOCl or NH2Cl without scavenging action on oxygen free radicals. Sulfhydryl group of taurine appears to show partially a protective action on HOCl-and NH2Cl-induced degradation.