Interval suction traps were used to study the attractant effect of CO2 and 1-octen-3-ol on trap catches of mosquito populations at 2 different locations in Florida. There was no significant increase in the numbers of mosquitoes caught when the concentration of CO2 was increased from 200 to 1,000 cc/min. One-octen-3-ol used by itself attracted mosquitoes in numbers similar to CO2 released at 200 cc/min. One-octen-3-ol and CO2 acted synergistically in attracting significantly greater numbers of Aedes taeniorhynchus, Anopheles spp. and Wyeomyia mitchellii than either bait used singly, although the response of Culex spp. to this bait combination was less pronounced. Ceratopogonidae (Culicoides furens) and Tabanidae (Diachlorus ferrugatus, Tabanus nigrovittatus and Chrysops spp.) were also attracted to the combined bait.