All-trans retinoic acid was evaluated in metastatic measurable non-small cell lung cancer. All-trans retinoic acid was given at 175 mg/m2 orally on a daily basis. Twenty-eight patients (median age 58, 16 males, 12 women) had an ECOG performance status of 0 (26 patients) and 1 (two patients). Sixteen of the 28 had no weight loss. Eleven had between 5 and 10% and only one had greater than 10% weight loss at time of entry. Toxicities included cutaneous (cheletis 25/28), fatigue (10/28), myalgias/anthralgias (9/28), and headache (17/28). Alterations in triglycerides and hepatic transaminases were noted in a majority of patients. Two partial responses occurred in patients with adenocarcinoma. Both responses were 7 months in duration. Activity of all-trans retinoic acid in metastatic non-small cell lung cancer is minimal, but due to its low toxicity profile it should be tested in setting with other agents.