Summary.-This report gives the 5-year findings of a double-blind study of longterm cytotoxic chemotherapy as an adjuvant to surgery in patients receiving busulphan or cyclophosphamide for carcinoma of the bronchus compared with a group receiving a placebo. Of 243 patients initially allocated busulphan, 234 cyclophosphamide and 249 placebo, 28%, 27% and 34%0 respectively were alive at 5 years. There were significant associations between mortality from bronchial carcinoma and histological involvement of the resected intrathoracic nodes and the histology of the tumour.Haematological toxicity, especially thrombocytopenia, was frequent and severe in the busulphan series, and low platelet counts continued long after chemotherapy was stopped.