A serologic survey for antibodies to arboviruses in serum from domestic animals, cattle and sheep, from the south of Portugal was done with the hemagglutination-inhibition (HI) test. The following viruses were used as antigens: Sindbis, chikungunya, West Nile, Central European tick-borne encephalitis (TBE), Israel turkey meningoencephalitis (ITME), Batai, and Ťahyňa. Of the bovine serum, 16% had HI antibodies to West Nile virus, with titers ranging from 1:20 to 1:5,120; and these specimens also reacted with the TBE antigen (5.1%) and with the ITME antigen (8.2%), but this reactivity was probably due to serologic overlap. None of the serum specimens after acetone treatment gave positive tests with the Sindbis or with the chikungunya antigens. The percentage of serum positive to the Batai and to the Ťahyňa antigens was 2% and 3% respectively.