Interleukin-2 (IL-2) and beta-interferon (beta-IFN) are biologic agents with antitumor activity observed in preclinical models. Some studies of patients with advanced non-small cell lung cancer treated with IL-2 report relatively long survival, despite low response rates. Seventy-six evaluable patients with stage IV non-small cell lung cancer were treated in a randomized Phase II study with either IL-2 alone or IL-2 plus beta-IFN. Patients received either IL-2 at 6 x 10(6) Cetus units/m2 3 days weekly or the combination of IL-2 at 5 x 10(6) Cetus units/m2 plus beta-IFN at 6 x 10(6) units/m2, both given 3 days weekly. Both biologic agents were administered by intravenous bolus injection on an outpatient basis. Objective responses were observed in 3/76 (4%)) patients. Grade 4 toxicity occurred in 3/39 patients treated with IL-2 alone, and in 4/37 patients treated with IL-2 plus beta-IFN. An additional lethal respiratory toxicity occurred in a patient who received IL-2 plus beta-IFN. The median survival of all patients treated on this study was 33 weeks. Despite producing only a 4% objective response rate. IL-2 appears to have a favorable impact on survival comparable to chemotherapy. The role for this immune therapy in the management of non-small cell lung cancer requires further study.