(BF Eldridge) Host preferences of Aedes aegypti for several vertebrate hosts were studied using a 2-port cage. Hosts were tested in pairs and the mosquitoes in the cage had the opportunity to choose either host. Mosquito probing was used as the criterion of host preference. Humans, guinea pigs, pigeons, and chickens were tested. Each species was compared with its own kind and with other species. Humans were most attractive. Guinea pigs were more attractive than chickens or pigeons. Among individual humans highly significant differences in attractiveness were observed. No significant differences were found in intraspecies tests with other hosts.