The purpose of the study was to investigate the antitumour activity and toxicity of high dose (120 mg m-2) single agent epirubicin therapy in untreated extensive small cell lung cancer patients. Out of 80 patients entered, 71 were evaluable for both antitumour activity and toxicity, 4 only for toxicity and 5 were lost for follow-up. The drug possessed a high antitumour activity, the overall response rate was 47.9% (34/71) with 4 complete remissions (CR) and 30 partial remissions (PR). The median remission duration was 3.5 months. Particular drug activity was observed in the primary tumours, lymph nodes and pleural metastases. Toxicity (leukopenia, anaemia, vomiting, reversible rhythmic cardiac disorder, stomatitis) was mild, alopecia was registered less than in adriamycin medication. One fatal congestive heart failure occurred. The actual mean survival time calculated on the basis of the data gained from 64 patients was 7.0 months (range 2-22). The high antitumour activity and no increase in toxicity justify the incorporation of high dose epirubicin into combination therapy.