The aims of this study were to investigate the effects of BAL collection on the respiratory function in healthy dogs and in dogs suffering from lower airway respiratory diseases and to consider the potential diagnostic value of some biochemical and cytological parameters measured in BAL fluids. For that, endoscopy and BAL collection were performed under anaesthesia induced with medetomidin (40 mu g/kg IM) and propofol (1 mg/kg IV) in dogs with pulmonary disorders (n = 30) and in healthy dogs (n = 10). The evaluation of the respiratory function was made throughout determination of blood gas and acid-base balance before anaesthesia and directly after BAL fluid sampling. In parallel, the effects of the anaesthesia alone on the respiratory system were also assessed in healthy dogs (n = 10) which were not submitted to the BAL collection. The anaesthesia protocol instead of the BAL collection by itself induced hypoventilation and low O(2) exchange between alveoli and arteries as evidencing by significant decreases of PaO(2) and O(2)Sat and significant increases of PaCO(2) and arterial-alveolar PO(2) gradient (A-aPO(2)). In diseased dogs. PaO(2)/O(2)Sat and the A-aPO(2) were initially affected and under anaesthesia, variations of O(2)Sat, PaCO(2) and base deficit were aggravated whereas changes in PaO(2) and A-aPO(2) were less pronounced compared to healthy controls. Significant increases of LDH. ALT and ALP activities and of urea concentrations in BAL fluids from diseased dogs coupled to a high cellularity (epithelial and inflammatory cells) and positive bacterial isolation in some cases have confirmed the inflammatory and/or infectious origin of the pulmonary diseases. Although biochemical and cytological analysis of the BAL fluids can help to characterize the pulmonary disease, its collection under anaesthesia may require some attention in diseased dogs because of its direct effects on respiratory function.