Objective: To evaluate the effect of cytotoxic chemotherapy on survival in patients with non-small cell lung cancer. Design: Meta-analysis using updated data on individual patients from all available randomised trials, both published and unpublished. Subjects: 9387 patients (7151 deaths) from 52 randomised clinical trials. Main outcome measure: Survival. Results: The results for modern regimens containing cisplatin favoured chemotherapy in all comparisons and reached conventional levels of significance when used with radical radiotherapy and with supportive care. Trials comparing surgery with surgery plus chemotherapy gave a hazard ratio of 0.87 (13% reduction in the risk of death, equivalent to an absolute benefit of 5% at five years). Trials comparing radical radiotherapy with radical radiotherapy plus chemotherapy gave a hazard ratio of 0.87 (13% reduction in the risk of death; absolute benefit of 4% at two years), and trials comparing supportive care with supportive care plus chemotherapy 0.73 (27% reduction in the risk of death; 10% improvement in survival at one year). The essential drugs needed to achieve these effects were not identified. No difference in the si Conclusion: At the outset of this meta-analysis there was considerable pessimism about the role of chemotherapy in non-small cell lung cancer. These results offer hope of progress and suggest that chemotherapy may have a role in treating this disease.