Allopatric and sympatric infections of <i>Lymnaea neotropica</i> and <i>Lymnaea viatrix</i> var. <i>ventricosa</i> with Argentinean and French isolates of <i>Fasciola hepatica</i> were carried out to determine the capacity of these snails to produce metacercariae and to verify if this capacity changed with snail generation. The same process was also made with a French population of <i>Galba truncatula</i> known to be highly susceptible to French isolates of the parasite. In each lymnaeid species separately considered, the survival rate at day 30 post-exposure and prevalence of <i>F. hepatica</i> infection in the group infected with Argentinean miracidia were significantly greater than those recorded in the corresponding French one. Compared to infected <i>G. truncatula</i>, both South American lymnaeids had longer patent periods and produced a higher number of metacercariae. The highest infections were noted with <i>L. v. ventricosa</i>. In the three snail species, metacercarial production was more important with the Argentinean isolate of miracidia than with the French one. If three successive generations of <i>L. v. ventricosa</i> are exposed to the same French isolate of miracidia, cercarial production significantly increased from parents to the F2 generation, while the other characteristics of infection only showed insignificant variations. <i>L. neotropica</i> and <i>L. v. ventricosa</i> are better intermediate hosts for French <i>F. hepatica</i> than local <i>G. truncatula</i>. The numerical increase of shed cercariae in the F1 and F2 generations of <i>L. v. ventricosa</i> demonstrates a rapid adaptation of this species to the French isolate of the parasite.Facultad de Ciencias VeterinariasCentro de Diagnóstico e Investigaciones Veterinarias