Hepatozoon species are apicomplexan parasites that infect blood cells and viscera of terrestrial vertebrates. One species, Hepatozoon clamatae, primarily infects green frogs, Rana clamitans, whereas another, Hepatozoon catesbianae, primarily infects bullfrogs, Rana catesbeiana, although both species of parasite are capable of infecting either species of frog. The aim of this study was to determine whether the basis for this partial host specificity is manifested at the gamont, or intraerythrocytic, stage of the parasite's life cycle. Blood was drawn from infected frogs and treated in vitro with a saline solution to induce intracellular gamonts to emerge from host erythrocytes. This treated blood was added to in vitro samples of uninfected blood of green frogs and bullfrogs. After 1 hr, samples were analyzed to determine the level of re-entry of the parasites into uninfected erythrocytes. Results obtained using multiple combinations of donor and recipient frogs indicate that extracellular gamonts of both parasite species do not exhibit preference for erythrocytes of 1 frog species over those of another. These results suggest that the basis for the observed host specificity is not determined at the gamont stage and is more likely dependent on another stage in the parasite life cycle.