The response of Microtus pennsylvanicus to traps with or without various prior occupants is described. Microtus were most frequently captured in traps previously visited by Microtus, but they showed a significant avoidance of traps previously visited by Blarina brevicauda. However, the probability of entry into such traps was no lower than into traps previously visited by other rodent species (Mus musculus, Peromyscus leucopus, or Zapus hudsonicus). There was an even lower probability of entry into traps which were previously empty. Blarina had a significantly higher probability of entering traps previously capturing Blarina than traps previously capturing Microtus or no one. We conclude that this evidence gives no support for the hypothesis that Blarina is a significant predator of Microtus pennsylvanicus.