Bronchoalveolar lavage (BAL) was first applied as a research tool to study local immune and inflammatory mechanisms. 1–3 As a diagnostic tool, BAL can serve as a ‘window to the lung’ to provide complementary information to histopathology from biopsies. BAL is a minimally invasive procedure and has become a powerful investigative tool of pulmonary medicine and a standard diagnostic procedure in patients with interstitial lung disease (ILD). 4–6 In a few of these diseases BAL findings have a specific diagnostic value and can replace lung biopsy. 6,7 The technique has several advantages over biopsy procedures: it is safe, virtually without morbidity, and collects samples from a much larger area of the lungs, therefore giving a more representative view of inflammatory and immunological changes. 8–14 Sometimes even a normal BAL may be useful to exclude some disorders with high probability (e.g. extrinsic allergic alveolitis, eosinophilic pneumonia, alveolar haemorrhage) and to focus attention in other directions. 5