The behaviour of poly(methylene N, N-dimethylpiperidinium chloride) in aqueous and methanolic solutions in the presence of tetraethylammonium bromide has been investigated by light scattering; the parameters characterizing the macromolecular chain have been calculated. Peculiar behaviour of the macromolecules in aqueous solutions was attributed to the influence of the simple electrolyte co-ion due to hydrophobic interactions.