Nosema eurytremae, a hyperparasite of trematode larvae, can easily be transmitted from one trematode species to another by feeding snails with spores. Hyperparasites from larvae of Postharmostomum sp. in the land snail Bradybaena similaris were transmitted to rediae of Echinostoma audyi and sporocysts of Trichobilharzia brevis in the freshwater snail Lymnaea rubiginosa. N. eurytremae were also transmitted to rediae of Fasciola gigantica in L. rubiginosa, of Echinostoma malayanum in Indoplanorbis exustus, and of Echinostoma ilocanum in Gyraulus convexiusculus from spores obtained from larvae of various species of trematode in L. rubiginosa and I. exustus. Attempts to transmit N. eurytremae to adult E. malayanum by feeding spores to rat hosts were unsuccessful.