1. This paper presents experimental evidence to show that Limnaea truncatula is not the only British snail susceptible to infection with Fasciola hepatica.
2. Of the six British species of Limnaea, five may be infected under laboratory conditions, L. auricularia proving resistant to infection. Full development of the parasite occurs in L. truncatula, L. slagnalis, L. palustris and L. glabra, while development as far as the production of rediae occurred on one occasion in L. pereger. Of the susceptible species L. truncatula may be infected at any age or size, but the other species are susceptible only during the first few days after hatching.
3. F. hepatica appeared to be relatively pathogenic to hosts other than L. truncatula even though the level of infection (as evidenced by the number of rediae which developed) was considerably lower than in the more usual host.