To determine if the chemotherapy resistance of non-small cell lung cancer could be modified by oral verapamil, 72 patients were entered into a randomised trial of verapamil plus chemotherapy vs the same chemotherapy alone. Verapamil 480 mg day-1 was given for 3 days starting 24 h prior to chemotherapy which consisted of bolus vindesine 7 mg followed by ifosfamide/mesna 5 g m-2 over 24 h, followed by mesna alone for a further 8 h. Cycles were repeated every 3 weeks for up to six courses. Sixty-six patients were eligible for tumour response analysis and responses occurred in 41% of those randomised to chemotherapy plus verapamil and in 18% of those randomised to chemotherapy alone (P = 0.057). Median survival from start of treatment was significantly better in the verapamil arm (P = 0.02). Toxicity of the combination of chemotherapy plus verapamil was principally neurological and was manageable. Thus the addition of oral verapamil to vindesine/ifosfamide chemotherapy is feasible and in this study was associated with improved outcome. Further confirmation of these observations is required in non-small cell lung cancer, a tumour characterised by resistance to conventional chemotherapy.