The purpose of this study was to investigate examine changes in venous blood gases of Brown Swiss calves with pneumonia. For this purpose, 30 calves exhibiting having clinical sings of pneumonia and 20 healthy calves were used. Venous blood samples were collected from the healthy and diseased calves before and after treatment with Draxxin (tulathromycin-Pfizer) in order to determine pH, pCO(2), pO(2). tCO(2) and HCO3 levels by Blood Gas Analyzer. Compared to the controls group, in the diseased animals, there was a significant increase of pCO(2) and HCO3 levels, together with a significant decrease of pH and PO2 levels (p<0.05). One week after treatment, pH, pCO(2) and HCO3 levels were significantly changed. Despite this change, these levels were still similar with other groups. Also, the venous blood pO(2) level went back increased to be statistically the same as the healthy animals. The tCO(2) level was not found statistically different among the three groups. It is concluded that pneumonia in calves impairs gas exchange, but that gas exchange improves rapidly after treatment.