The ’catalytic’ effects of polyzwitterions on aqueous inter-ionic reactions were studied through the analysis of the influence of a representative zwitterionic macromolecule, poly(diethyl-(2-methacryloyloxyethoxy-2-ethyl)-1 -(3-sulfopropyl) ammonium betaine], on two model inter-anionic and inter-cationic reactions, i.e. oxidation of ferrocyanide by persulfate and aquation of a bromopentaalnminecobalt complex. The anionic system is clearly accelerated, but considerably less than with a cationic polyelectrolyte of similar structure, poly[triethyl-(2-methacryloyloxyethoxy-2-ethyl)-ammonium methylsulfonate. A small model zwitterion, (C2H5)(3)-N+-(CH2)(3)-SO3-, has no effect. The inter-cationic reaction is not accelerated by the polyzwitterion.