Three iron-5,10,15,20-tetraarylporphyrins (Fe(Por-Ar-4), Ar = 2,3,5,6-tetrafluro-N,N,N-trimethylanilinium (1), N,N,N-trimethylanilinium (2), and p-sulfonatophenyl (3)) have been investigated as catalysts for the dismutation of chlorite (ClO2-). Degradation of ClO2- by these catalysts occurs by two concurrent pathways. One leads to formation of chlorate (ClO3-) and chloride (Cl-), which is determined to be catalyzed by O=Fe-IV(Por) (Compound II) based on stopped-flow absorption spectroscopy, competition with 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonicacid), O-18-labeling studies, and kinetics. The second pathway is a concerted dismutation of chlorite to dioxygen (O-2) and chloride. On the basis of isotope labeling studies using a residual gas analyzer, the mechanism is determined to be formation of O=Fe-IV(Por)center dot(+) (Compound I) from oxygen atom transfer, and subsequent rebound with the resulting hypochlorite ion (ClO-) to give dioxygen and chloride. While the chlorate production pathway is dominant for catalysts 2 and 3, the O-2-producing pathway is significant for catalyst 1. In addition to chlorite dismutation, complex 1 catalyzes hypochlorite disproportionation to chloride and dioxygen quantitatively.