Over 340,000 mosquitoes were collected in the Northern Territory between January 1982 and November 1992, and tested for the presence of arboviruses. Identifications of one hundred and seventeen (117) alpha and flavi viruses included forty two (42) Ross River virus, seventeen (17) Barmah Forest virus, fifty (50) Sindbis virus, four (4) Kunjin virus and one (1) Murray Valley encephalitis virus. The remaining three (3) flaviviruses are unknown but were not Kunjin or Murray Valley encephalitis. The isolations of alpha and flavi virus were from six (6) species of mosquitoes, representing 248,224 individuals of the total mosquitoes collected. Most viruses were isolated in the January to April period with RRV and Sindbis more frequent in February, Barmah Forest more frequent in March, and Kunjin more frequent in May. Ross River virus was isolated from Cx. annulirostris (22), Ae. normanensis (16), Ae. vigilax (2), Ae. notoscriptus (1) and Ae. phaecasiatus (1). Barmah Forest virus was isolated from Ae. normanensis (6), Ae. vigilax (6) and Cx. annulirostris (5). Sindbis virus was isolated from Ae. vigilax (2), Ae. normanensis (4), Ae. lineatopennis (1) and Cx. annulirostris (43). Kunjin and MVE were isolated only from Cx. annulirostris.