A total of 142 bass (54 Micropterus dolomieu and 88 Micropterus salmoides) were collected April through September 2000 and April through July 2001 from 5 locations in Gull Lake, Michigan, U.S.A., and examined for Proteocephalus ambloplitis. Proteocephalus ambloplitis was 100% prevalent in both smallmouth and largemouth bass. The numbers of P. ambloplitis from each microhabitat (gonads, liver, spleen, mesentery, pyloric ceca, intestine) were counted and compared between females and males within and between host species. Overall mean intensity of infection and mean intensity in the ovaries was significantly higher in smallmouth bass. Infections among smallmouth bass were most intense in the gonads but most intense in the liver and mesentery among largemouth bass. Given the known pathology of P. ambloplitis, bass tapeworm may reduce the reproductive potential of smallmouth bass in Gull Lake.