Summary Nine hundred and one wild-animal serum specimens (amphibian, reptilian, avian, and mammalian) from St. Lawrence County, New York, were examined by hemagglutination-inhibition and neutralization techniques for evidence of Eastern and Western encephalomyelitis, Powassan, St. Louis encephalitis, Maguari, and Cache Valley arbovirus reactivity. Group A antibody was infrequent. One Chrysemys p. picta serum had detectable EE neutralizing antibody, and a 1:20 serum dilution inhibited hemagglutination of EE antigen. Five mammalian serum specimens (one Lepus americanus, two Marmota monax, and two Vulpes fulva) demonstrated WE neutralizing antibody. Group B antibody was relatively frequent. Both serologic techniques (N and HI) detected POW antibody among 52 specimens representing nine mammalian species: one Erethizon dorsatum, one Lepus americanus, 38 Marmota monax, one Mephitis mephitis, two Mustela frenata, three Procyon lotor, two Sciurus carolinensis, one Tamias striatus, and three Tamiasciurus hudsonicus. One Rana pipiens pipiens serum showed monotypic SLE antibody by HI and N techniques. Arbovirus antibodies for groups A and B were rare among the 192 specimens of human serum, but EE, WE, POW, and SLE neutralizing antibodies were detected in four. Bunyamwera group reactivity was found only with human serum, of which 5% neutralized CV virus of the BUN group.