Of the 3 respiratory tract disease syndromes that occur in birds associated with Escherichia coli infection, acute colisepticemia, characterized by hyperemic and swollen viscera, tended to occur in young birds. Subacute fibrinopurulent serositis involving air sacs and pericardium was more common in older birds. Chronic granulomatous pneumonitis was not seen as flock epornitics but as chronic disease in birds dying in small numbers some time after one of the previously mentioned forms of the disease. Serotypes of 100 E coli isolates from turkey colibacillosis revealed most to be O1, O2, O36, or O78. Virulence of the isolates, as conducted by IV inoculation of 6-week-old turkeys, showed O78 strains to be highly virulent and O36 strains to vary in virulence.