As the ecolocation system of the vampire bats (Desmodus rotundus) is not very efficient, these animals very likely use their sense of vision for orientation over long distances. To get an impression of the environment, they must be able to distinguish different visual patterns. In this paper the ability of two vampire bats to discriminate between two simple signs (white vertical stripe vs. white circle of same area) was investigated. To determine which oriteria of the patterns are used for the discrimination these signs were altered in different respects. Of all the different criteria the animals evaluated most strongly the “vertical impression” of the vertically arranged bar. A horizontal arrangement of the bar reversed the choice: the bats selected in this case the negative circle.