Th e signifi cance of different species of freshwater gastropods in transmission of polyxenic trematode species on the territory of Ukrainian Polissya is reviewed, with emphasis on instances of the specificity of trematode parthenogenetic generations to their mollusk hosts. For some hosts of polyhostal trematode parthenitae, the leading part in sustaining the local and regional populations of certain trematode species is confirmed. Groups of the common hosts also play an important role in circulation of these helminthes. In adverse conditions, populations of some trematode species can persist using the secondary and subsidiary hosts. The rare and accidental hosts of certain trematode species do not have a significant effect on their transmission.