Thirteen patients with unresectable non small cell lung cancer were treated with radical radiotherapy and carboplatin administered concurrently. The first 6 patients were treated to a total dose of 60 Gy in 30 fractions in 6 weeks, with carboplatin 70 mg/m2/day on days 1 to 5 during weeks 1 and 5 of radiotherapy. The remaining 7 patients were given 60 Gy in 30 fractions in 3 weeks, treating twice a day (accelerated fractionation). Carboplatin was given as above but only during week 1 of radiotherapy. Twelve patients completed radiotherapy without interruption but 2 patients developed WHO grade 3 neutropenia. Major toxicity was oesophagitis, one patient requiring nasogastric feeding. Average duration of dysphagia (any grade) in the accelerated fractionation group was 21 weeks. Four patients achieved good partial responses even though initial tumour volume was large. We conclude that this treatment is associated with increased but acceptable early mucosal toxicity.