The relatively high incidence of E. coli infection among diseased chickens (56.7%) indicates the role of this organism as a potentially important avian pathogen in Egypt. Such incidence among healthy chickens was found to be 26.7 %.

Serogroups O 11l: K 58 (B 4) was the most predominant isolates obtained from diseased chickens (57.6 %), followed by serogroups O 127: K (B 8) in an incidence of 29.4 %. The least serogroups recovered were O 1119 and O 128.

From apparently healthy chickens, the following serogroups were recorded O 119, O 18, O 124 and unidentified E. coli in order of their frequency.

The isolated serogroups were markedly resistant to ampicillin, streptomycin, tetracycline and trimethoprim sulfamethoxazole, but completely sensitive to flumequine, gentamicin and nitrofurantoin.

The clinical signs, post-mortem findings, mortality rate and re-isolation observed among one-day old chicks infected experimentally per os with 0.5 ml of broth containing 3 X 108 viable different seroproups of E. coli for 2 successive days were discussed in detail.