The 15-year findings are presented of a double-blind, randomised study planned in 1964 in which cytotoxic chemotherapy with either busulphan or cyclophosphamide prescribed to be given daily for 2 years as an adjuvant to surgery was compared with placebo in the treatment of 726 patients with carcinoma of the bronchus. The two cytotoxic agents administered in this way did not influence survival. At 15y, 8% of the 243 patients allocated busulphan, 9% of the 234 cyclophosphamide, and 10% of the 249 placebo were alive, these being 10% of the patients who had had epidermoid cancers, 12% large-cell, 5% small-cell, 5% adenocarcinomas, and 8% other histological types. The study provides data on long-term results in a large group of patients who were, in effect, treated by surgery alone. Survival was significantly shorter in patients with histological involvement of the resected intrathoracic nodes (log-rank test P much less than 0.001). A finding of particular interest is that the histological type of the tumour did not influence survival in the 390 patients whose nodes were not involved, although, as expected, it did in the 336 whose nodes were involved, the 226 with epidermoid cancers surviving longer than the 57 with small cell carcinoma, the 31 with adenocarcinoma and all 110 with non-epidermoid carcinomas (P much less than 0.001 in each comparison).