 Diffuse lung disease DLD remains a challenging area for diagnosis and treatment. Features suggestive of the various histological subtypes of DLD can be obtained from the clinical history and examination, and can also seen on cross-sectional imaging high resolution computed tomography HRCT scanning, however final diagnosis very often relies on the results of more invasive testing. The gold-standard diagnostic tool is the surgical lung biopsy, but this requires a general anaesthetic and either thoracoscopy or thoracotomy. The morbidity and even mortality attached to this approach in these patients, many of whom have significant respiratory compromise, has resulted in less invasive techniques being employed in many instances. At present, this involves the use of bronchoalveolar lavage BAL and transbronchial biopsies via the fibreoptic bronchoscope. BAL can be distressing for patients if there is spill-over of lavage fluid into the larger airways, and transbronchial biopsies lead to significant bleeding or pneumothorax in around 5 of patients. Even with biopsies and BAL, some patients still progress to surgical lung biopsy. 