The degree to which host suitability is a reflection of host community structure in generalist parasites was studied experimentally in the common fish acanthocephalan Leptorhynchoides thecatus. Previous study has shown that green sunfish (Lepomis cyanellus) are required, and largemouth bass (Micropterus salmoides) are suitable (but not required) hosts, where they occur sympatrically in natural communities. The present study examined populations of L. cyanellus and M. salmoides held separately in mesocosms and exposed to L. thecatus cystacanths via laboratory-infected Hyalella azteca (Amphipoda). Recruitment, maturation, and transmission of worms were examined over a 17-wk period and compared between fish species. Infections with L. thecatus were found as early as 2 wk after the introduction of cystacanth-infected amphipods, and by week 11 fishes of both species harbored gravid worms. Immature worms were observed in both host species by week 17 and were presumed to be a result of natural egg production and release resulting in infections of amphipods and the subsequent reinfection of fish. No significant difference in the prevalence, abundance, percentage of worms gravid, or time of parasite maturation was found between host populations. Results indicate that the different roles played by these host species in the maintenance of L. thecatus supra-populations in natural systems are not due to intrinsic factors but rather to differences in host autecology and community structure.