Clinical-, serological and pathological examinations were conducted on twenty feedlot cattle with acute pneumonia from the Department ofLima, in order to determine the etiology ofthe disease. Prior to sacrifice ali the animals were monitored for clinical signs and sera samples taken for serological testing. At postmortem, ali affected lungs were examined grossly and pathological samples were taken to identify viral agents by direct immunoflourescence and/or bacteriological isolation, as well as for histopathological studies. Ali effected animals exhibited fever (39.41-41.8º C), tearing, coughing, tachipnea and watery to mucupurulent nasal discharge. Sorne ofthese animals (n=9) had dyspneic breathing with open mouth, lingual protrusion and abundant salivation, where as others (n= 11) had moderate to severe thriftiness. At necropsy, fibrinous lobar pneumonia involving ventral regions of the apical, intermediate and diaphragmatic lobes was found in ali the animals. Histological analyses found eleven cases of acute suppurative bronchopneumonia (Bronchitis, bronchiolitis and al veo litis) and nine cases of fibrinous pleuritis and interstitial pneumonia. Etiopathogenesis studies documented the presence ofmultiple viral agents plus Pasteurella. Among these, Bovine pestivirus (BVD) was the most common, followed by Bovine Herpes virus-1 (BHV-1, n= 15)), Bovine respiratory Syncytial virus (BRSV, n=7) and Parainfluenza type (PI-3, n=5). In 95% ofthe cases (n= 19) virus and bacteria (up to 3 pneumopáthogens) were found coexisting in the same affected tissue, with BVDV and BHV-1 plus Pasteurella the most frequent combination. Pasteurella micororganisms were isolated In 55% (n=l l) ofthe cases and P. multocida was the most frequented identified. The presence of multiple viral agents was corroborated by the detection of antibodies against BRSV and PI-3 in ali the animals tested, as well as the presence ofantibodies to BVD in 80% (n=l6) and BHV in 75% (n=l 5) ofthe sample.