Although several investigators have presented data suggesting that the Caprifoliaceae is polyphyletic in origin, the family has been retained as a taxon in recent classifications. Serological analyses of the taxa included within the family have been undertaken to provide additional taxonomic data. Precipitin techniques of double diffusion (Ouchterlony) and nephelometry (Boyden Procedure) were used to analyse serological similarities of seed proteins from representatives of the family. Three distinct groupings were detected for the taxa included in the Caprifoliaceae. AlthoughViburnum exhibited greatest serological similarity withSambucus, Viburnum was quite distinct from all members of the family investigated.Sambucus also was somewhat distinct from the other genera and exhibited about as much serological correspondence withCornus of the Cornaceae as with any tested member of the Caprifoliaceae. The remaining species examined formed a very close serological grouping. These data can be interpreted as supporting either a monophyletic or polyphyletic origin of the family as presently composed, because of the different arrangements of the families Caprifoliaceae and Cornaceae in the various systems of classification.