The role of combination chemotherapy in the treatment of advanced non-small-cell lung cancer is controversial. At best, a small survival benefit can be achieved. Therefore, other treatment modalities are needed. On the basis of the promising treatment results with interleukin-2 (IL-2) -containing immunotherapy in renal cell cancer and melanoma, we performed a phase I-II study with IL-2 and interferon alpha (IFN-alpha). Eligible patients were treated with IL-2 18 x 10(6) IU/m2/day by continuous intravenous infusion (c.i.v.) for 3 days. On the same days, 5 x 10(6) U/m2/day IFN-alpha was given intramuscularly. After a rest period of 4 days, patients at the first dose level received IL-2 2.4 x 10(6) IU/m2/day c.i.v. for a period of 28 days, followed by 14 days' rest, 14 days' treatment, 7 days' rest, and a final treatment for 14 days. Patients at the second dose level were treated according to the same schedule, in which the dose of IL-2 was increased to 3.6 x 10(6) IU/m2/day. During low-dose IL-2 treatment, patients received IFN-alpha 5 x 10(6) U/m2/day on days 1 and 4 of each week. Eleven patients were admitted to the study, six at the first and five at the second dose level. Median age was 54 years; all patients had a performance status of 0 or 1. The most important adverse effects included anorexia, fatigue, nausea, and headache, which were not dose limiting. In the 11 patients treated, no responses were seen. Nine patients developed progressive disease during the first 5 weeks of treatment. We concluded that this regimen of IL-2 and IFN-alpha is ineffective.