One hundred and sixty eight birds were collected from 4 broiler flocks in Assiut farms (governmental and private)from both live and freshly dead  birds, aging between 4-6 weeks. The clinical signs showed swelling of heads with conjunctivitis and some birds were with closed eyes, nasal discharge and diarrhea was also noticed  in some cases. The causative bacterial agents could isolated only from the sinus and the upper respiratory tract. 150 isolates were recovered from 168 cases, 76 isolates, 24, 20, 14 isolates Pseudomonas aeruginosa, 8 Klebsiella, 6 isolates Proteus, and 2 isolates Staphylococcus aureus. The pathogenicity of E. coli, Mycoplasma gallisepticum and  Haemophilus paragallinarum to 4 weeks old broiler birds free from any bacterial infection revealed appearance of depression, conjunctivitis, sneezing, nasal discharge within 3-4 days post inoculation. Injection of birds by Mycoplasma gallispeticum and E. coli in combination with bad hygienic condition,  birds showed signs within 24 hours post inoculation in the form of nasal discharge, sneezing, abnormal sounds, facial oedema, swelling in the infraorbital sinuses, conjunctivitis, abnormal ocular secretion and diarrhea. The postmortum of dead cases revealed septicaemia, severe enteritis, perihepatitis, congestion of the lung, air saculitis, sinusitis, tracheitis, pericarditis and caseous material in the nasal passages. Histopathological studies of the chickens experimentally infected with M. gallisepticum and E. coli revealed pathognomonic changes in the cutaneous and subcutaneous tissue of periocular skin and eyelids, liver, lung and intestine.