The object of this dissertation was to investigate the respiratoryproblems affecting calves with special reference to bacterial etiologicalagents, and to discuss the best methods of treatment and control ofthese diseases.Our study was conducted on two localities atDakahlia Govemorate including Shoha and Aga breeding farms, a total of one handred and twenty diseased and forty apparently normal calves housed in the fore mentioned areas were examined.Representive samples of whole blood, serum and nasal swabs aswell as lung specimens were obtained and investigated according tothe clinical signs. Thus haematological, biochemical, bacteriological, post-mortum and histopathological studies had been carried on the collected samples as well as chemotherapeutic trials among pneumonic animals in comparison with the auto-control groupThe clinical picture of diseased calves included typical signs of bronchitis and bronchopneumonia which was described in details and discussed.The cytological studies of whole blood samples involved red and white blood cells counts, differential leucocytic count, haemoglobin content, as well as blood gases and acid-base balance of both diseased and apparently healthy calves.