The effects of the acanthocephalan parasite Pomphorhynchus laevis on the behavior of its crustacean intermediate host, the amphipod Echinogammarus stammeri, were studied. A drift study revealed that infected amphipods were disproportionately represented in drift samples taken throughout a 24-hr period; infection with more than 1 parasite enhanced this effect. Infection also interacted with the daily timing of drift, with parasitized amphipods beginning to drift earlier in the evening. Two distinct behaviors quantified in laboratory settings may play a role in this increased drifting behavior: parasitized amphipods showed (1) an increased preference for an illuminated environment and (2) increased activity in comparison to nonparasitized conspecifics. These results are consistent with previous studies on the effects of P. laevis on another amphipod host, Gammarus pulex, and provide new data on the activity level of P. laevis-infected amphipods.