Biomphalaria peregrina was found to be naturally infected with cercariae of Zygocotyle lunata in a pond of the Zoological Garden of Buenos Aires. Mice and chicks were fed metacercariae and gravid adults recovered. Eggs recovered from mice feces were used for experimental infections. Laboratory-reared B. peregrina and 4 other Biomphalaria spp. were successfully infected with Z. lunata miracidia. Biomphalaria glabrata was refractory. Species of Helisoma, the only intermediate hosts of Z. lunata so far reported, have never been found in Argentina. Species of Biomphalaria may be intermediate hosts of Z. lunata in the southern region of the Paraná River Basin.