The feasibility and efficacy of treating patients with locally recurrent or metastatic non-small cell lung cancer (NSCLC) or head/neck cancer with interleukin-2 (IL-2), cisplatin, and 5-fluorouracil (5-FU) was tested. Treatment was given every 28 days and consisted of cisplatin, 100 mg/m2 on days 1 and 8; 5-FU, 1,000 mg/m2 by continuous infusion on days 1-3; and IL-2, 12 million units/m2 by i.v. bolus on days 15-19. Thirty-four patients (22 NSCLC, 12 head/neck cancer) were registered in the study. The median age was 58 years; 59% had Karnofsky performance status of 70-80% and over one-half received prior therapy. All patients were evaluable for toxicity and 29 (18 NSCLC, 11 head/neck cancer) were evaluable for response. Twenty-five patients experienced at least one grade 3 or 4 toxicity, but these toxicities were transient and, in general, well tolerated. The response rate was 37% for NSCLC (0 complete response, 7 partial response) and 55% for head/neck cancer (2 complete response, 4 partial response). Two patients with head/neck cancer responded to treatment after failing prior therapy with cisplatin/5-FU alone. The combination of IL-2, cisplatin, and 5-FU is tolerable and active for treatment of NSCLC and head/neck carcinoma; the combination may not be cross-resistant with other chemotherapy combinations. Further studies of IL-2 combined with cisplatin/5-FU are warranted to determine the most effective dose and schedule.