Patients with advanced head and neck squamous cell carcinoma (HNSCC) are severely immunocompromised. In virtually all such patients who have been studied, reduced numbers of circulating CD3+ T-cell-receptor (TCR)alpha/beta+ T lymphocytes, a reduction of natural killer (NK) activity, and a poor induction of lymphokine-activated killer (LAK) cell activity (following in vitro treatment with recombinant interleukin-2 [rIL-2]) have been detected. Recently, however, it has been demonstrated that perilymphatic injections of low doses of rIL-2 may induce a local reduction of tumor masses in these patients. The present study, a cooperative pilot effort on the clinical effects of this route of administration, showed an activation of the lytic machinery in lymphocytes belonging to the T-cell lineage, as well as a potentiation of NK activity in the peripheral blood. These findings demonstrated that the severe immunodeficiency of HNSCC patients may be at least partially corrected by in vivo administration of rIL-2.