The study aims to investigate the lung expression of some positive acute phase proteins (APPs) such as CRP (C reactive Protein), SAA (Serum amyloid A) and SAP (Serum amyloid P) and of the cytokine TNF-alpha and its receptor according to the pneumonia severity in sheep and goats. After conventional histopathology, the lung tissue samples were classified according to the intensity of the inflammatory reaction during pneumonia into 3 groups (mild forms mainly characterized by hyperaemia and oedema in alveoli, moderate forms associating mild necrosis and inflammatory infiltrates in alveoli, bronchioles and bronchus and severe forms in which the inflammatory reaction associated intense necrosis, oedema and neutrophil infiltrates in all parts of lung), each group containing 10 cases (5 sheep and 5 goats) and then, the APP and cytokine expression in lung was evaluated by immunohistochemistry using specific primary antibodies in the all diseased animals and in 10 healthy ruminants (5 sheep and 5 goats). The immunoreactivity for all the investigated markers was greatly exacerbated in pneumonic lungs compared to the controls. Whereas the mean CRP expression was significantly higher and a strong immunolabelling was more frequently encountered in the mild forms than in the aggravated ones, the mean expression of the other selected markers was significantly increased in the moderate (except for the TNF-alpha) and severe forms compared to the mild forms and a strong immunoreactivity (except for the TNF-alpha and its receptor for which a moderate immunoreactivity was observed in 2 sheep and 2 goats) was evidenced in all animals from the 2 groups. This study demonstrated that acute phase proteins are produced in pneumonic lungs and are important markers for detecting the earliness (CRP) and the severity (SAA, SAP, TNF-alpha and TNF-alpha receptor) of pneumonias in sheep and goats.