We have employed cyclic voltammetry and controlled-potential electrolysis to explore the catalytic reduction of diphenyl disulfide by electrogenerated cobalt(I) salen in acetonitrile containing various tetraalkylammonium salts as well as tetraphenylphosphonium bromide. Cobalt(I) salen reacts with diphenyl disulfide in an outer-sphere electron-transfer reaction to produce the radical-anion of diphenyl disulfide, which breaks apart to form benzenethiolate and a benzenethiyl radical. This latter radical is much easier to reduce than diphenyl disulfide and can accept another electron homogeneously from either the radical-anion or electrogenerated cobalt(I) salen to give benzenethiolate. Such a mech anistic picture is unlike that found earlier for the catalytic reduction of halogenated organic compounds by electrogenerated cobalt(I) salen. In the course of this investigation, we have discovered that, when electrolyzed solutions containing benzenethiolate are removed from the electrolysis cell and injected directly into a gas chromatograph for analysis, a reaction occurs in the injector port between benzenethiolate and the tetraalkylammonium (or tetraphenylphosphonium) moiety of the supporting electrolyte to give an alkyl phenyl sulfide and a trialkylamine (or diphenyl sulfide and triphenylphosphine). As part of this research, we have examined the direct reduction of diphenyl disulfide at glassy carbon cathodes, and we have determined the lifetime of the radical-anion of diphenyl disulfide.