The spontaneous polymerization of 4-vinylpyridinium p-styrene-sulfonate or 4-vinylpyridinium chloride with sodium p-styrenesuifonate or of 4-vinylpyridinium 2-acrylamido-2-methylpro-panesulfonate with sodium p-styrenesuifonate produces an amphoteric, equimolar copolymer. An UV study on the interaction between 4-vinylpyridinium chloride and sodium p-styrenesulfonate indicates an absorption maximum corresponding to 1:1 charge transfer complex. From the observed results, a charge-transfer polymerization of 4-vinylpyridinium salts with electron-donating monomers is elucidated.