Chlorinated ethylenes, (CE), specifically perchloroethylene (PCE) and trichloroethylene (TCE), are widespread groundwater pollutants listed as EPA priority pollutants. The catalytic dechlorination of CE by a water soluble porphyrin, tetrakis-(4-carboxyphenyl)-porphyrin cobalt, (TCPP)Co, was studied and had superior aqueous phase dechlorination activity. The CE dehalogenation catalytic cycle was elucidated with kinetic, spectroscopic, and synthetic studies. The CoI porphyrin species was active for dehalogenation through studies with UV-visible absorbance spectroscopy and cyclic voltammetry. Evidence for chlorovinyl complexes as potential catalytic cycle intermediates was obtained through the preparation of (TPP)Co(trans-C2H2Cl) and (TPP)Co((Z)-C2HCl2) and the observation of (TCPP)Co(C2HCl2) by MS. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005).