Gemcitabine is a novel nucleoside analogue with activity in solid tumours. This study assessed the objective response rate to gemcitabine given weekly intravenously at a dose of 1250 mg/m2 for 3 weeks followed by 1 week of rest (one cycle) in chemonaive patients with inoperable non-small cell lung cancer (NSCLC). 161 patients with NSCLC were recruited from 10 sites in nine countries. Most patients had stage IIIb (31.3%) or IV (64.6%) disease, and 93.8% had a performance status of 0 or 1 according to the WHO scale. Of 151 evaluable patients, there were 3 complete responses and 30 partial responses lasting at least 4 weeks for an objective response rate of 21.8% (95% CI 15.5-29.3%). All responses were validated by an extramural Oncology Review Board. The mean duration of response was 8.8 months. The mean survival for all patients (16.1% of patients still alive 26 months after last patient started treatment) was 11.5 months. Improvements were also observed in secondary efficacy parameters such as performance status, weight, analgesic requirement, pain, and other disease-related symptoms including cough, dyspnoea, haemoptysis, anorexia, somnolence and hoarseness. Haematological and non-haematological toxicity was mild given the biological activity of gemcitabine. This study confirms gemcitabine as one of the most active agents in NSCLC with the added benefit of a modest toxicity profile and ease of administration on an out-patient basis. Gemcitabine is a suitable candidate for combination chemotherapy in patients with NSCLC.