The Galerucella nymphaeae species complex is a controversial group of leaf-consuming beetles with a Holarctic distribution. It includes several closely allied species or forms living in different habitats and utilizing different food plants. In northern Europe, two species are encountered, G. nym phaeae (L.) living on Nuphar, and G. sagittariae (Gyllenhal) living on semiaquatic or terrestrial plants, while all North American forms have been so far considered conspecific with the European G. nymphaeae. In the present study we have compared chorion polypeptides of the northern European G. nym phaeae and G. sagittariae with North American G. nymphaeae collected from Nuphar. The northern European G. nymphaeae was found to differ from both northern European G. sagittariae and North American G. nymphaeae, which were found to be virtually identical in respect to their chorion polypeptides. The present results, coupled with earlier data concerning e.g. egg morphology, structure of larval cuticle, and comparison of several life history traits, demonstrate that northern European G. nymphaeae and North American G. nymphaeae are not conspecific, and that the North American G. nymphaeae may be more closely allied to the northern European G. sagittariae.