Thirty-four patients with previously untreated advanced non-small-cell lung cancer were treated with a combination of polychemotherapy and recombinant interferon. Chemotherapy consisted of cyclophosphamide, 400 mg/m2, epidoxorubicin, 50 mg/m2, and cisplatin, 40 mg/m2 (CAP) i.v. on day 4; recombinant alpha 2b interferon (r alpha 2b IFN) was given i.m. daily at the dose of 3-5 MU from days 1 to 7. The treatment was repeated every 4 weeks. In the 32 eligible patients the overall response rate was 19.3% (95% C.L. 7.4-37.4%). Non-hematologic toxicity consisted formerly in flulike symptoms and fatigue complained of by 37.5% and 31.2% of patients, respectively, and vomiting reported in 68.7% of patients; grade III-IV myelotoxicity was observed in 12.5% of cases. In no case was the toxicity life threatening. The median overall actuarial survival and progression-free survival were 37 and 20 weeks, respectively. This study indicates that the combination of CAP chemotherapy and r alpha IFN is feasible and active in the treatment of advanced non-small-cell lung cancer.