Establishment, survival and distribution of Leptorhynchoides thecatus (Acanthocephala) were investigated in largemouth bass, Micropterus salmoides, fed 10, 25, or 40 cystacanths and examined at 1, 3 or 5 weeks post-infection. Worms established widely in the alimentary tracts of bass but by 5 weeks post-infection had localized in the pyloric caeca and intercaecal region. Other individuals moved to parenteral sites where they remained immature, though viable. In the 10- and 25-level exposures, establishment and survivorship in the alimentary tract were roughly proportional to the dose of cystacanths. After 1 week post-infection in the 40-level exposure class, numbers of worms in the alimentary tract decreased significantly and parenteral occurrence increased significantly. Total survival of L. thecatus appeared to be density-independent. Maturation of worms was retarded temporarily as intensity of infection increased, but by 5 weeks post-infection worms from all doses were at roughly the same stage of development within sex. The caeca and intercaecal area apparently did not differ in their suitability for maturation.