Host-selection patterns of mosquitoes were determined over a 1-yr period at Abu Heif, a village in Sharqiya Governorate, Egypt, that has had a history of Rift Valley fever virus (RVFV) transmission. Culex pipiens L. and Cx. antennatus Becker were the most common mosquito species collected, and 8,252 blood meals from both species were analyzed by a precipitin technique. Host availability was estimated by a monthly census of human and animal populations. Both mosquito species exhibited opportunistic endophagic behavior. In bedrooms, 79% of Cx. pipiens fed on humans, compared with 53% of the Cx. antennatus. In animal sheds, 35% of Cx. pipiens and 68% of Cx. antennatus fed on sheep or goats. Cx. pipiens was primarily anthropophilic (forage ratio = 2.7) whereas Cx. antennatus was mainly an ovine feeder (forage ratio = 2.4). These findings indicated that both species probably were involved in the transmission of RVFV in Sharqiya Governorate during the epidemics of 1977 and 1978, Cx. pipiens being mainly responsible for transmission to humans, and Cx. antennatus for transmission among domestic animals. The persistent custom of keeping sheep and goats inside human dwellings, combined with the opportunistic host selection by the local mosquitoes, continues to make this area receptive to RVFV transmission.