A serologic study was conducted to investigate the exposure of captive and free-flying Canada geese (Branta canadensis) to five arboviruses, chlamydiae and Mycoplasma gallisepticum. Of more than 1200 serums screened in the metabolic-inhibition test (MIT), no serums neutralized eastern encephalitis virus (EEV), less than 1% neutralized western (WEV) or Venezuelan (VEV) encephalitis viruses, 2% neutralized St. Louis encephalitis virus (SLEV), and 29% neutralized California encephalitis virus (CEV). Supplementary serologic procedures indicated that a nonspecific inhibitor probably caused inhibition of CEV in the MIT. Fifty-six per cent of 197 serums had hemagglutination-inhibition titers of 1:80 or higher against M. gallisepticum and were considered “positive”. Two hundred and eight serums were negative for complement-fixing antibody against chlamydiae.