Flanders virus was recovered from 75 pools of mosquitoes----36 Culiseta melanura, 8 Culex pipiens, 25 Cx. restuans, 3 Cx. salinarius, 2 Cx. (Culex) species, and 1 Coquillettidia perturbans----in Connecticut. Virus has been isolated each year from 1969 through 1978. Minimum field infection rates for the 10-year period were higher in 3 ornithophilic species---Cs. melanura (1:465), Cx. pipiens (1:435), and Cx. restuans (1:306) than in 2 general feeders--Cx salinarius (1:773) and Cq. perturbans (1:26666). Virus was demonstrated in mosquitoes collected during the months of June, July, August, and September, and isolation rates followed the population curves for Cs. melanura and Culex (Culex) species. Flanders virus was not recovered from 84,632 adult female mosquitoes of species other than Culiseta, Culex, and Coquillettidia; from 13,767 adult males mosquitoes including 2912 Culiseta spp., 4445 Culex spp., and 143 Cq. perturbans, from 9791 reared from larvae mosquitoes (mostly Aedes spp.), or from 47,034 hematophagous flies other than mosquitoes.