Over 180,000 mosquitoes were collected in the Top End of the Northern Territory between January 1982 and June 1985, and tested for the presence of arbo viruses. Thirty-one isolates of alpha and flavi virus were made and positive identifications included fifteen Ross River virus, eleven Sindbis virus and three Kunjin virus. The remaining two flavi viruses are unknown but were not Kunjin or Murray Valley Encephalitis. The isolations were from four species of mosquitoes, representing 124,756 individuals of the total mosquitoes collected. Aedes normanensis yielded ten isolates of Ross River virus and one isolate of Sindbis, Aedes notoscriptus yielded one isolate of Ross River, Aedes vigilax yielded one of Ross River, while Culex annulirostris yielded ten
isolates of Sindbis, one of Ross River and three of Kunjin. These isolations add significantly to the number of
isolations of toga viruses from mosquitoes in the Northern Territory.