We describe the case of a 52-year-old Japanese woman with advanced adenocarcinoma of the lung, in whom once-daily treatment with 250 mg ZD1839 ('Iressa') demonstrated a marked antitumour effect. She had initially achieved a partial response with cisplatin-based combination chemotherapy, but had subsequently progressed and had failed to respond to salvage chemotherapy. She had also received whole-brain irradiation for brain metastases. On admission, the patient was confined to bed due to dyspnoea and had rapidly progressing hypoxia secondary to lymphangitis carcinomatosa and a massive right pleural effusion. She was treated with oxygen supplementation and oral ZD1839, which, within a week, led to marked tumour regression and gradually improving dyspnoea. The main adverse event observed was a grade 2 rash. A month after starting ZD1839 treatment, the patient was discharged without the need for oxygen supplementation and had since returned to full-time work. This is a demonstration of ZD1839 producing a dramatic clinical response when administered to a patient with poor performance status who had received extensive prior treatment with cytotoxic agents.'Iressa' is a trademark of the AstraZeneca group of companies.