BACKGROUND: Alveolar pattern of the lung field is usually caused by several lung involvements such as edema, hemorrhage and pneumonia, but differentiation using radiography is usually impossible. Objectives: Evaluation of HU and lung pattern of pneumonia in dogs using CT-scan technique and confirmation by CT assisted FNA as a safe diagnostic procedure. Methods: In this study, 10 dogs with respiratory distress suspected for pneumonia were selected and radiography and CBC were used for evaluation of lung pattern and cytology. Before and after contrast medium injection, CT-scans of the lung field were achieved. Finally, in transverse CT sections, FNA of involved lung lobes was taken for cytologic evaluation. After the confirmation of pneumonia, CT scans were reevaluated with more attention and pulmonary pattern was described and HU of involved regions was measured. Results: In all of the patients, ventral region of the lungs, especially cranial and middle lung lobes were involved and the involvement of the left lungs was prominent. The mean HU of the unhealthy lung parenchyma before contrast medium study was between 31 and 39, and after contrast study was between 46 and 70. It means the HU has been significantly increased. Also, the contrast of the involved lung regions was increased which helped to differentiate the unhealthy lung tissue from the adjacent soft tissues. Hematology tests in all of the patients were representative of infection. Conclusions: Both CT-scan and CT assisted FNA from the lung are beneficial and practical methods for the diagnosis of pulmonary disorders such as pneumonia