Carboplatin has been incorporated into a new low toxicity combination chemotherapy regimen with methotrexate and vinblastine (CVM) against small cell lung cancer (SCLC). We have compared CVM (carboplatin 300 mg/m2, vinblastine 6 mg/m2, methotrexate 30 mg/m2, all intravenously every 4 weeks) with ACE (doxorubicin 40 mg/m2, cyclophosphamide 600 mg/m2, etoposide 100 mg/m2 all intravenously day 1-3, every 3 weeks) in a randomised trial. 36/54 evaluable patients treated with CVM achieved an objective response (67%) (95% confidence limits [CL] 54-79%) compared with 44/50 treated with ACE (88%) (95% CL 80-97%, P = 0.06). For patients with limited disease treated with CVM, 14/17 (83%) (95% CL 64-100%) had an objective response compared with 14/15 (93%) (95% CL 81-100%) treated with ACE (not significant). Overall median survival was 8 months for CVM and 7 months for ACE. Haematological toxicity was significantly lower for CVM than ACE and consequently dose reduction/delay and infection were less with CVM. Subjective toxicity was low and alopecia was significantly less for CVM than ACE. CVM is an active, well tolerated new chemotherapy regimen for SCLC.