4-Demethoxydaunorubicin (4-DMDR) is an orally active analog of daunorubicin that in preclinical testing has demonstrated greater antitumor activity and less cardiotoxicity than its parent compound. Thirty-two patients with metastatic non-small cell lung cancer received 4-DMDR at a dose of 40-50 mg/m2 orally every 21 days. Thirteen patients had received no prior chemotherapy. Among the 30 adequately treated patients, one major response lasting 5.2 months was observed. Leukopenia 10-14 days after treatment was the most commonly observed toxicity. With an overall observed major response rate of 3.3% in 30 patients, the predicted true response rate is less than or equal to 16% (p = 0.05). At the dose and schedule studied in this group of patients with non-small cell lung cancer, 4-DMDR had only marginal activity.