To compare irinotecan (CPT-11)+gemcitabine vs CPT-11 alone as second-line treatment for patients with advanced non-small cell lung cancer (NSCLC) progressing after docetaxel-cisplatinum-based therapy. A total of 147 evaluable, pretreated patients, with NSCLC, received either gemcitabine (1000 mg m(-2), days 1 and 8)+CPT-11 (300 mg m(-2), day 8) (Group A, n=76) or CPT-11 (300 mg m(-2), day 1) (Group B, n=71), every 3 weeks. All patients were evaluable for response and toxicity. The objective response rate was 18.4% (95% CI: 9.71-27.14%) and 4.2% (95% CI: 0-8.90%) (P=0.009) for groups A and B, respectively. No significant differences between the two groups in terms of the median duration of response, time to tumour progression, overall survival and 1-year survival were observed. The CPT-11/gemcitabine regimen significantly improved the patients' quality of life ('general mood today' (P=0.014), 'coughing' (P=0.003) and 'intensity of symptoms' (P=0.034)) compared with CPT-11. More cycles had to be delayed (P=0.001) and required prophylactic growth factor support (P=0.001) in Group A than B. Three (3.9%) patients in Group A and eight (11.3%) in Group B developed febrile neutropenia (P=0.09); one patient died of sepsis in each group. Three additional (Group A, n=1; Group B, n=2) treatment-related deaths were observed. Grade 3-4 haematologic toxicity was comparable in the two groups except anaemia (P=0.03 in favour of CPT-11). Other nonhaematologic toxicities were mild and similar in the two groups. CPT-11+gemcitabine resulted in a higher response rate and better control of disease-related symptoms than CPT-11 alone, but without any improvement in the overall survival.