Forty-one patients with advanced non-small cell lung cancer (NSCLC) were entered into a phase II study of high dose recombinant interferon (rIFN)-beta. Patients received intravenous (i.v.) rIFN-beta on a Monday, Wednesday, Friday schedule with a weekly dose escalation until > or = grade 3 toxicity or 720 x 10(6) IU/dose was achieved. Thirty-eight patients were eligible. Seventeen patients received the highest planned dose of rIFN-beta and 11 experienced dose-limiting toxicity at lower doses. Ten patients developed progressive disease before grade 3 toxicity was reached. There were no objective responses observed. Significant and dose-limiting toxicities included nausea and vomiting, fever, rigors, severe dyspnea, hypotension, and hypertension. IFN-beta has no measurable antitumor activity against NSCLC even at maximum tolerated doses (MTDs).