Microhabitat use of Allocreadium lobatum (Trematoda) in the intestine of creek chub (Semotilus atromaculatus) was studied using natural infections. Seventy-six creek chub harboring only A. lobatum in their intestine provided data on the position of 212 worms along the length of the intestine. Positions of worms within the intestine co-varied strongly with host size and therefore intestinal length; worm positions standardized by intestinal length eliminated this relationship. Analyses of standardized worm positions (worm location) revealed that microhabitat use did not vary with worm size, maturity, or number of eggs in the uterus. Individuals of A. lobatum occurred throughout the intestine, but were concentrated in the posterior 30% of the intestine, regardless of demographic properties of the worms themselves. Standardized niche breadths of parasite infrapopulations suggested strict microhabitat specificity, but nearest-neighbor analyses revealed very little aggregation of worms in infrapopulations beyond what is expected by chance. Overall, trematodes of this species appear to exhibit some microhabitat specificity when examined with snapshot, field-collected data, but there is no clear indication of what mechanism might produce the observed pattern. Use of the intestine by individuals of A. lobatum might be more dynamic than can be revealed by the present investigation or studies similar to it.