Respiratory disease conditions are continuing to cause heavy economic losses in the poultry industry. Since Dec. 1991 respiratory manifestation with different clinical courses have been observed in poultry flocks in different countries. Bacteriological examinations have resulted in isolation of pleomorphic gram-negative rods (PGNR). The detected bacteria were designated as Ornithobacterium rhinotracheale gen. nov., sp. nov. in the rRNA-Superfamily V. The present paper reviews the literatures related to ORT current situation on isolation and identification, serotyping of ORT as well as differential diagnosis from other similar bacterial infections.