Intrathoracic histiocytomas are rare lesions, believed to be localised areas of reactive granulomatous inflammation. They nearly always arise in lung parenchyma or pleura. This is the first reported case in which a histiocytoma arising in a major bronchus has been demonstrated radiologically.A.C., an 11-year-old white boy, presented to out-patients with an attack of wheezing with cough and haemoptysis in June 1972. There were no previous chest symptoms and he had no family history of asthma. He was noted to have a few loud rhonchi on deep inspiration. The chest radiograph at that time was normal. At his next attendance four weeks later he reported one further episode of haemoptysis and was still wheezing. Treatment with sodium cromoglycate and orciprenaline elixir was started.