Tallimustine binds to the minor groove of DNA where it alkylates the N3 position of adenine and may interfere with gene transcription. We conducted a phase II trial of Tallimustine given at a dose of 750 micrograms/m2 intravenously every 4 weeks in patients with small cell lung cancer progressing or relapsing following cisplatin or carboplatin-based chemotherapy. We treated 14 eligible patients with a performance status 0, 1 or 2, bi-dimensionally measurable disease and adequate end-organ function. The main toxicity was neutropenia with a median granulocyte count of 0.1 x 10(9) per liter (range 0-3.9) and four patients (27%) developing febrile neutropenia. In addition, most patients (93%) experienced lethargy. No objective responses were seen. A mixed response was seen in one patient and three others had stable disease for a median of 3.7 months. We conclude that Tallimustine is an ineffective agent in previously treated small cell lung cancer.