Serum from 2,294 wild birds, 128 mammals, 22 reptiles, and 96 amphibians caught from May 1965 to June 1966 in Israel were examined for antibodies against Eastern equine encephalomyelitis. Semliki Forest, Sindbis, Langat, Israel turkey meningoencephalitis, and West Nile (WN) viruses by hemagglutination-inhibition (HI) tests. The incidence of positive serum was 14.4% for wild birds, 5% for mammals, and 9% for reptiles. No antibodies were detected in the amphibian serum; 73% of the positive avian serum had antibodies against group B viruses. The rest of the positive serum was divided among that positive for group A and that positive for both group A and group B viruses. Serologic conversions in sentinel chickens confirmed the activity of WN virus in the Hadera region during the period studied. Use of acetone extraction followed by kaolin treatment of serum minimized the number of falsely positive results obtained in the HI tests. Good correlation was found between results obtained in HI tests and indirect fluorescent-antibody staining of WN antigen among serum samples from 116 Columbidae examined by these two methods.