This study was carried out on a total of 40 animals (13 female cows, 14 cow bull and 13 cow calves of both sexes) with an age ranged from 1- 5 years. Animals were admitted to Zagazig Veterinary Teaching Hospital, Faculty of Veterinary Medicine, Zagazig University, Egypt with a history of injection site lesions. A history of injection at the site lesion was noted with swelling ranging from 5 to 15 cm in diameter, others were showing fluctuating swelling. Various clinical signs as abnormality in gait, painful condition on thigh, gluteal and neck muscle were recorded with respect to the site of lesion. Diagnosis was based on history, Clinico-biochemical findings, needle aspiration, ultrasound and histopathology of biopsy samples. Upon diagnosis, animals were classified into three groups; group I (Control group, n= 10), group II (Muscular abscess group, n= 17), and group III (Suppurative myositis group n= 13). Hematological findings revealed mild anemia, leucocytosis and neutrophilia in muscular abscess and suppurative myositis groups, while biochemical findings included hyperglobulinemia, elevation of serum muscular enzymes; aspartate aminotransferase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH) as well as a significant increase in C-reactive protein (CRP) and fibrinogen in both diseased groups in comparison to control group. Results of ultrasonographic examination in muscular abscesses group revealed homogenous echogenic content surrounded with hyperechoic capsule which is embedded in the muscle and an increase in the echogenicty of the muscle in suppurative myositis group. Histopathological examination of the biopsy specimen from the affected muscle revealed fibrinopurunlent inflammation with aggregation of dead and live neutrophils, hyaline degeneration of muscle and muscle edema. In conclusion, ultrasonography provides an accurate, non-invasive and fast technique for diagnosis injection site lesions. In addition CRP and fibrinogen values in association with total white cell count were very useful in the diagnosis and prognosis.