This study was carried on 80 native c ow calves in a large farm belonging to Cooperative Comittee forAnimal Producetion, Abu Hammad in Sharkia Province.These animals were classified, according to the clin- ical symptoms, into 4 groups, each of them contained20 calves as follow:- First groups:Were apparently clinically normal calves kept as control. Second group: Exhibited respiratory d.isorders. Third group: Represented by calves suffering from sporadic diarrhea.Fourth group:Were calves that exhibited skin lesion that proovedto be ringworm. Blood samples wer~ collected from clin-ically normal and diseased calveg to evaluate the level of serum GUT, S. GPT, LDH, alkaline and acid phosphata- bses, cholinesterase (in plasma & RBCs) , amylase and lipase; The study of the biochemical analysi$ showed the following points:- as abortify1ng organisms as they were isolated in a pre- dominant percentage from animals with retained placentaafter abortion than after fulLt’berm birth3. Twenty four cases revealed no bacteria. However, the higher frequency of bacteria in the majority of cases gave the consideration that bacteria is not a single factor in the problem. 4. Special recommendation w