Vampire bat rabies is one of the greatest deterrants to the raising of livestock in Latin America. To know more of the epizootiology of the disease as well as to understand the ecology of the vampire bat family, Desmodontidae, detailed information about their feeding habits and host preferences is essential. Vampire bats feed exclusively on blood. Examination of probable host animals for bat bites has been the primary method used to determine their victims. More reliable precise data are achieved by serological analyses of the digestive tract contents of vampires killed after attacking their hosts. Precipitin test techniques were used similar to those devised for the identification of blood meals of bloodsucking arthropods (Weitz, 1952, 1956, 1960; Tempelis & Lofy, 1963). If the exact domestic as well as wild animal host preferences of vampire bats were known, this knowledge could assist in their control and might indicate other hitherto unsuspected hosts.