The kinetics of the reaction of 10-phenylphenothiazine (PH) cation radical (PH-+) with pyridine (Py) have been examined. Electrochemical characterization of the PH/PH-+ couple in neat Py showed PH-+ to be of sufficiently low reactivity to permit kinetic investigation in this medium. The results of these kinetic determinations, together with those obtained in acetonitrile solutions of Py, indicate the applicability of a half-regeneration mechanism. The reaction gives rise to only the pyridinated product in neat Py while both'hydrolysis (sulfoxide) and pyridination products are observed in acetonitrile solutions. Formation of the sulfoxide is accounted for by the hydrolysis of an N-S bonded dicationic intermediate in the proposed pyridination mechanism. The product distributions observed in the pyridinations of the cation radicals derived from PH and other EE substrates reflect the relative reactivities of the corresponding dicharged intermediates.