Four strains of eastern equine encephalomyelitis virus were isolated from 16,731 adult female Culiseta melanura collected in Connecticut from 1969 through 1978. Two of the isolates were from mosquitoes collected during a widespread epizootic of this virus among equines and domestic birds in the state during 1972. Western equine encephalomyelitis virus, subtype II, was isolated for the first time in Connecticut in 1972. Three strains were recovered from Cs. melanura and one from the blood of a Rufous-sided towhee (Pipilo erythrophthalmus). Group A arboviruses were not detected in 140,915 adult female mosquitoes other than Cs. melanura, 13,767 adult male mosquitoes including 2,390 Cs. melanura, in 9,791 mosquitoes reared from immature stages, or in 47,034 other hematophagous Diptera.