Thirty-six patients with unresectable squamous cell carcinoma of the head and neck were entered into a phase Ib trial evaluating the toxicity, maximally tolerated dose (MTD), and immunomodulating effects of locally administered interleukin-2 (IL-2). Patients received daily IL-2 injected perilesionally in divided doses in each of four quadrants and bilaterally into the superior jugular lymph nodes. The dose of IL-2 began at 200 U/day and was escalated to 4 × 106 U/day in groups of six patients. Overall, regionally administered IL-2 was well tolerated. The most frequently encountered toxicities were fever, hepatotoxicity, and hypotension. Dose-limiting toxicity was encountered at 4 × 106 U. Of the 36 patients treated, 2 partial responses were noted at 2,000 and 4 × 106 U. We conclude that regionally administered IL-2 is well tolerated in patients with head and neck cancer and that the MTD is 2 × 106 U/day, similar to what has been reported with systemically administered IL-2. Although the overall response rate was low, it may be improved with prolonged administration of IL-2 or by combining it with other biologic or cytotoxic agents.