Host feeding patterns of mosquitoes were assessed through the identification of 865 blood meals collected from Brisbane during 2000-2001. Under natural conditions, mosquito feeding (including that of Culex annulirostris, Aedes vigilax, and Aedes notoscriptus) was primarily on dogs (37.4%), but also on birds (18.4%), horses (16.8%), brushtail possums (13.3%), humans (11.6%), and cats, flying foxes, and macropods, depending on site. From 1997 to 1999, sera (N=1706) were collected from dogs, cats, horses, flying foxes, and brushtail possums in the Brisbane area and were analyzed by microneutralization assay for antibodies to Ross River virus (RRV) and Barmah Forest virus (BFV). For RRV, all vertebrate species tested had been naturally infected, and seroprevalence varied from 10.5% to 25.5%, whereas for BFV, rates varied between 0% and 11.3%. Brushtail possums were often infected in the field, with 17.6% and 10.7% of wild individuals having antibodies to RRV and BFV, respectively. Horses and flying foxes also had a relatively high prevalence of antibodies to RRV. This study, therefore, provides data to indicate that brushtail possums play a role in the urban transmission of RRV in Brisbane and that horses, when they occur, also fill the same role.