The various manifestations of poultry diseases associated with Escherichia coli have been recently reviewed (20). The etiology and pathogenesis of the disease, with special reference to 0 groups concerned, were studied by workers in the U.S.A. (2,5,11) and Great Britain (14,21) and on the Continent (19,22). Although the disease has been recognized in Canada, no serological identification of strains has been published. This paper reports biochemical and serological findings of E. coli strains of avian origin isolated mainly in Ontario (95%). A considerable increase in the incidence of disease associated with E. coli has become evident in Ontario. Perhaps this is due, in part, to increased awareness of the disease entities described in the literature (7,8,10,12,13,20). There is little doubt that colisepticemia and other E. coli disease syndromes are difficult to define because of their complex pathogenesis (1,4,6). In this respect, an effort was made to isolate strains of E. coli from cases in which it was considered significant as a cause of disease, as done by workers in Great Britain (21). The association of certain carbohydrate fermentation patterns, particularly of dulcitol and salicin, was studied in relation to the virulence of the organisms (15,18).