Four prospective randomized trials were undertaken to evaluate single-drug chemotherapy after resection of bronchial carcinoma in men. The drugs studied were mechlorethamine hydrochloride, cyclophosphamide, and methotrexate. A total of 2,348 curative resections were carried out; 1,172 patients received adjuvant therapy after the resection and 1,176 underwent operation alone. The accumulated five- and ten-year survival rates were 24.8% and 13.5%, respectively, for the treatment group and 26.2% and 16.3% for the control group. The differences were not significant. It is therefore apparent that single-drug adjuvant therapy is not beneficial in the management of patients who have undergone a curative resection of a bronchial carcinoma. Involvement of lymph nodes in the specimen was associated with a significantly poorer prognosis, but cell type, other than oat cell, appeared not to affect the prognosis when a curative resection had been carried out.