Collections with CDC Gravid Mosquito Traps on 954 trap-nights from May through September 1983 are compared to 2,608 concurrent resting site collections made in the same area of Memphis, Tennessee. Gravid Traps yielded 88 times more Culex per collection and 96 times more Culex per man hour. The total Gravid Trap catch was 135,724 mosquitoes, 99% of which were either Culex pipiens or Cx. restuans, whereas these species comprised only 63% of the 6,613 mosquitoes collected from resting sites. Gravid Traps also collected significant numbers of Aedes aegypti and Ae. triseriatus. On most nights, more than 95% of mosquitoes in the Gravid Trap catch were gravid females. These results demonstrate that the trap is an effective and efficient device for collecting several important vector species. The preponderance of gravid mosquitoes should enhance the probability of encountering pathogens acquired by blood-feeding.