The frequency with which the 4 virus-vector species of longidoroid nematodes occurring in Britain transmitted their associated plant viruses was compared in a series of experiments using a standard procedure. In these tests X. diversicaudatum proved an effective vector of British isolates of arabis mosaic virus and strawberry latent ringspot virus and L. attenuatus of an isolate of tomato black ring virus from England. In comparison, isolates of raspberry ringspot virus and tomato blackring virus from Scotland and of raspberry ringspot virus from England were transmitted much less readily by their respective vectors, L. elongatus and L. macrosoma. These differences in ability to transmit virus were not related to differences in feeding access to the virus source- or bait-plants, in the extent to which virus was retained within the nematode feeding apparatus or in the frequency with which virus was recovered from Longidorus in concurrent slash tests. 3 Scottish isolates of raspberry ringspot and tomato blackring viruses were transmitted equally infrequently by 2 populaions of L. elongatus and the frequency with which virus was transmitted was not greatly increased when the species of source- or bait-plants was changed.