Between April 1988 and December 1992, 37 patients with small, previously unirradiated, primary non-small cell carcinomas of the bronchus causing symptoms due to endobronchial disease were treated at the Christie Hospital, Manchester, with a single fraction of high dose rate intraluminal radiotherapy (ILT) using the microSelectron-HDR machine. Small primary (SP) lesions were defined as being less than 2 cm in diameter in a direction perpendicular to the central axis of the iridium-192 treatment source. Fifteen patients (41%) were treated to a dose of 15 Gy and 22 patients (59%) to 20 Gy at a distance of 1 cm from the central axis of the source. At 6 weeks following ILT, improvement in symptoms was seen in the following percentages of patients: haemoptysis 96%, pulmonary collapse 69%, cough 55% and dyspnoea 52%. The magnitude of improvement in these symptoms was largely maintained in patients surviving to 4 months and then 12 months post-ILT. Median actuarial survival was 709 days, 2-year survival 49.4% and 5-year survival 14.1%. Overall, there was no significant difference in survival after treatment with 20 Gy compared with 15 Gy at 1 cm. At the close of study, there were four patients still alive without disease recurrence with survivals of 38, 48, 49 and 63 months. All had had biopsy-proven squamous cell carcinomas and all had been treated with 20 Gy at 1 cm. Five patients died from massive haemoptysis as a terminal event at 4, 9, 9, 10 and 11 months post-ILT, well below the median survival for this group of patients. Again, all had been treated with 20 Gy as opposed to 15 Gy at 1 cm. Over the same time period, 287 patients with non-small cell carcinomas of more than 2 cm in diameter (large primary lesions, LP), were treated with a single fraction of ILT only, as their initial treatment. A consistently greater percentage of patients with SP lesions showed an improvement in the symptoms of haemoptysis and pulmonary collapse when compared with patients with LP lesions. Patients with LP lesions demonstrated a decreased actuarial survival when compared with SP lesions, with median survival being 156 days, 2-year survival 3.1% and no survivors beyond 39 months. This study demonstrates that, in patients with small endobronchial carcinomas a single fraction of ILT can give efficient palliation of symptoms and lead to long term disease-free survival, but that a dose of 20 Gy may be at the limit of bronchial radiation tolerance for a single dose technique employing a high dose rate source.