We report a randomized multicentre study of split-course radiotherapy (RT), with or without combination chemotherapy (CT), in 238 patients with inoperable non-small cell lung cancer (NSCLC), previously untreated, confined to one hemithorax and the mediastinal nodes. In both treatment groups RT consisted of 55 Gy in 20 F given over 7 weeks with a 3-week rest interval. CT consisted of the 3-drug regimen CAP: C = cyclophosphamide 400 mg/m2, A = adriamycin 40 mg/m2, P = cisplatin 40 mg/m2; 2 cycles of CAP given before RT, one during the rest interval and six after RT. Seventy per cent in the RT arm and 67% in the RT-CT arm had epidermoid carcinoma. No significant difference was apparent between the RT and the RT-CT arms with respect to objective response rates (CR + PR) (44 and 49%, respectively), median duration of response (278 and 320 days), local failure (31 and 20%), distant progression (23 and 20%) or median survival (311 and 322 days). The survival figures showed an almost significant (P = 0.05) therapeutic advantage of the combined regimen with stage IIIM0 disease. Progressive disease was the cause of death in 92% and 88%. We conclude that chemotherapy did not contribute significantly to either local control or survival as compared to radiotherapy alone.