Water soluble, amphoteric optical brighteners (W) comprising at least one brightener-characteristic radical X which contain at least one anionic substituent and covalently linked over at least one tertiary amino group Z to at least one non-chromophoric, essentially aliphatic, polyquaternary ammonium-hydrocarbon radical Y containing more than one quaternary ammonium group and in which each hydrocarbon radical is optionally interrupted by and/or substituted with one or more further heteroatoms, have surprising brightening properties, especially in papermaking, and in the form of their aqueous solutions are of notable stability.