Aedes aegypti (L.), Culex sitiens Weidemann, Culex annulirostris Skuse, and Culex quinquefasciatus Say mosquitoes colonized at the Queensland Institute of Medical Research, Brisbane Australia, were fed on blood containing Barmah Forest virus (BF). Only Cx. annulirostris was susceptible to infection, with a median cell culture infectious dose (CCID50) of 10(3.36) per mosquito. Ae. aegypti and Cx. quinquefasciatus were infected experimentally, but at rates of < 9%. Cx. sitiens did not become infected. Infection rates for Cx. annulirostris fed 10(3.5) CCID50 of virus per mosquito, varied from 9 to 50% between 2 and 13 d after infection. Virus transmission to suckling mice by Cx. annulirostris occurred from 2 d after infection. Transmission of BF virus by Cx. annulirostris was 10% at 2 d after infection and did not exceed 8% thereafter. Although Cx. annulirostris may be infected and is able to transmit BF virus to suckling mice, it is nonetheless a relatively inefficient vector of the virus.