For some years Dr. Herman N. Bundesen, chairman of the Epidemic Committee of the National Foundation for Infantile Paralysis, Inc., has believed that a coordinated and systematic field study of the epidemiology of poliomyelitis should be undertaken by a single group of well trained persons over an extended period. The opportunity for the beginning of such a study presented itself in the summer of 1945 when a special survey of poliomyelitis was organized in Chicago.1A case finding program was undertaken to (a) establish, if possible, the amount of unrecognized poliomyelitis in urban communities, (b) determine the relative incidence of the paralytic and nonparalytic forms of the disease, (c) investigate contact between cases in the spread of urban poliomyelitis and relate this, if possible, to the various age groups, (d) evaluate the roles of the nose, throat, mouth and feces, if any, in the transfer of the virus from