The novel nucleoside agent gemcitabine has demonstrated antitumor activity against a variety of solid tumors and is associated with low toxicity. A phase I trial in Germany of gemcitabine combined with the alkylating agent ifosfamide has shown encouraging activity against non-small cell lung cancer. The efficacy and toxicity of this combination was further evaluated in a phase II trial involving chemotherapy-naive patients with non-small cell lung cancer (mostly stage IV disease). Gemcitabine was administered at a dose of 1,000 mg/m2 on days 1, 8, and 15, followed by a 1-week rest, while ifosfamide was given at a dose of 1,500 mg/m2 on days 8 through 12. Fifty-five patients were treated, 49 of whom are evaluable for response. Six patients were not evaluable because they had not received sufficient therapy (less than one complete cycle) because of early disease progression or early death. Twelve patients responded, for an overall objective response rate of 24.5%. The median survival time was 8.9 months, and the 1-year survival rate was 30.9%. Grades 3 and 4 neutropenia occurred in 30.2% and 24.5% of patients, respectively, but the incidence of infection was low. These results indicate that the combination of gemcitabine and ifosfamide is active against non-small cell lung cancer and has a mild toxicity profile, and suggest that further evaluation of this combination is warranted.