The response to cisplatin in non-small cell lung cancer (NSCLC) is limited by the renal and neurological toxicities of this agent. Carboplatin has modest activity in NSCLC and when given in conventional doses has a different spectrum of toxicity. Both drugs were administered to 76 eligible patients with advanced NSCLC. No patient had been previously treated with chemotherapy. Cisplatin 50 mg/m2 and carboplatin 350 mg/m2 were administered every 28 days until disease progression occurred. There was 1 complete response and the overall response rate among the 68 evaluable for response patients was 13%. Neither histological subtype nor initial performance status was a significant factor influencing response. Median survival was 5.1 months with significant differences based on initial performance status but not on histological subtype. Severe or life-threatening leukopenia and thrombocytopenia occurred in 23% and 36% of the 76 patients, respectively. There were 2 toxic deaths, 1 each due to infection and haemorrhage. The efficacy of this combination is not different from that of carboplatin alone, and the combination may be of greater benefit in patients with more responsive tumours than NSCLC.