60 broiler checkens were used for this study. They were divided equally into three groups. They were experimentally infected with pasteurella multocida, E.Coli and Pasteurella multocida and E.Coli respectively. All chickens in the first group infected with P. multocida died 24-48 hours post infection. Pathological studies in this group revealed acute septicemic lesions. In the second group infected with E.Coli and P.multocida, the lesions tend to be subacute or chronic. Only 30% of chickens in this group died from acute pasteurellosis. In all chickens of the third group (infected with E.Coli only) chronic proliferative inflammation was observed in the lung and serous membranes. In conclusion, E.Coli infection protected 70% of chickens from acute septicemic pasteurellosis and prevent their sudden death.