Fifteen consecutive patients with advanced squamous bronchogenic carcinoma, most of whom had had radiotherapy, were given palliative photodynamic therapy, using either haematoporphyrin derivative or dihaematoporphyrin ether to light sensitize their tumour. All tumours responded to treatment by subsequent light at 630 nm and in the 12 patients where adequate tumour illumination was achieved there was complete clearing of the bronchus in three and partial (more than 50 per cent clearing) in the remaining nine, with relief of haemoptysis and/or breathing obstruction. One patient with recurrent tumour in a pneumonectomy stump after radiotherapy has remained disease-free for over two years since photodynamic therapy. The main complications were temporary skin light sensitization reaction in three, infection after reaeration of lung tissue in two, and transient but severe worsening of breathing obstruction in two.