Parasite-free snails of the genus Physa were experimentally infected with the miracidia of Posthodiplostomum minimum, the metacercariae of which were originally obtained from bluegills, Lepomis macrochirus. Twelve species of fish representing 5 families (Cyprinidae, Cichlidae, Centrarchidae, Poeciliidae and Ictaluridae) were exposed to cercariae from the infected snails. Two sunfish hybrids (female green sunfish, L. cyanellus X male redeal' sunfish, L. microlophus; and female bluegill X male redeal') were also exposed to cercariae of P. minimum. Only members of the family Centrarchidae became infected. Moreover, only the bluegill and its hybrid contained metacercariae in substantial numbers.