Bronchoalveolar lavage (BAL) is a diagnostic procedure used to recover cellular and non-cellular components of the epithelial lining fluid from the alveolar and bronchial airspaces. Two types of the procedure have been described: bronchoscopic and non-bronchoscopic BAL. The preferred site for bronchoscopic BAL is the middle lobe or the lingula. Gentle manual or mechanical aspiration is applied in order to collect the lavage specimen in the collection trap, while the tip of the flexible bronchoscope is maintained wedged in the bronchus of the selected lavage site. The parameters measured in BAL fluid (BALF) include the percentage of the instilled normal saline that is recovered as well as various BALF cellular and non-cellular components. BAL is performed for diagnostic, therapeutic and research purposes. The most common indication for BAL is the investigation of lower respiratory tract infection. In chronic interstitial lung disease, BAL may have an important role in reaching a specific diagnosis, characterizing alveolitis, and monitoring patients during treatment and follow-up. BAL is still considered the gold standard for diagnosing chronic pulmonary aspiration. In general, BAL is a well-tolerated and safe procedure; however, on occasion, cough, transient wheezing and pulmonary infiltrates have been observed, which usually resolve within 24 h.