We investigated the activity and toxicity of gemcitabine as a single agent in patients with advanced non-small cell lung cancer (NSCLC) after recurrence or failure of previous treatment with a platinum-containing regimen. From November 1995 to October 1997, 83 patients (73 men and 10 women) with stage IIIB or IV NSCLC received gemcitabine 1,000 mg/m2 on a weekly x 3 every 4 weeks schedule. Responses were assessed every two treatment courses. The median age of the patients was 63 years. Eastern Cooperative Oncology Group performance status was 0-1 in 62 patients; 2 in 21 patients. The predominant histology was squamous (39 patients); 49 patients had stage IV disease and 34 patients had stage III disease (33 stage IIIB and I stage IIIA). Sixteen patients (19%) achieved a partial response to treatment; the median duration of response was 29 weeks (range, 6 to 50 weeks). Treatment was well-tolerated: leukopenia and thrombocytopenia World Health Organization grade 2-3 occurred in 23% and 20% of patients, respectively. Mild asthenia was observed in 16% of patients and peripheral edema was observed in 5% of patients. Nausea and vomiting were present in 16% of patients. In this study, gemcitabine showed significant activity in a patient population usually associated with poor prognosis. This finding suggests a possible role for gemcitabine as second-line treatment in patients who have recurring disease or who have failed a platinum-containing regimen, and in the absence of significant toxicity.