This article gives the degradation rate constants of meso-tetrakis(3,5-disulfonatomesityl)porphinatomanganese(III) X (where X = H2O and/or OH- depending on pH) (MnTMSP) and its beta-brominated analogue (MnTMSPBr8) toward the oxidants NaOCl, H2O2, and (CH3)(3)COOH at various pHs, I = 0.2 M and 30 degrees C.In addition, the degradation rate constants of MnTMSP was determined when it was bound to cationic supports - namely, CTAB, a poly(vinylbenzyltrimethylammonium chloride) latex, 2,6-ionene and 2,10-ionene. MnTMSP showed high structural stability toward the peroxides in strong acidic medium and the degradation rate constants were found as low as 10(-4) min(-1) at pH < 1.50. When NaOCl was employed as the oxidant, the pH dependence of the stability of MnTMSP was vice versa and its degradation rate constant was determined as 1.43 X 10(-4) min(-1) at pH 14.10. In strong acidic solution, the supports CTAB and latex made the stability of MnTMSP toward the peroxides improve significantly. In strong basic solution, only latex-bound MnTMSP showed higher stability toward NaOCl than the homogeneous MnTMSP. Because MnTMSPBr8 was not stable in solutions having pH higher than 9 and containing no oxidant, its stability was investigated at pH < 9 and it showed slightly lower stability toward the peroxides than the non-brominated analogue. (C) 2000 Elsevier Science B.V. All rights reserved.