To study whether regional injection of recombinant interleukin 2 (rIL-2) can induce an in vivo lymphocyte activation in cervical lymph nodes (LNs) of patients with head and neck carcinoma, 12 patients, candidates for prophylactic dissection, were treated for 7-10 days prior to surgery with rIL-2, 10(5) units/day, injected in the perimastoid region. A marked induction of cytotoxic activity against allogeneic (K562 and Daudi lines) and autologous target cells (fresh spindle cell carcinomas of the tongue) was observed in lymphocytes obtained from jugular, spinal, and, to a lesser extent, submandibular LNs of all treated patients. An increase of cytotoxicity was also present in LNs contralateral to the rIL-2 injection side. On the other hand, only a borderline increase in spontaneous proliferation was detected. Moreover, in the two cases tested, a marked and apparently autologous tumor (Auto-Tu)-specific lysis was found in CD5+ lymphocytes obtained from LNs, whereas lymphokine-activated killer activity was mainly exerted by CD16+ natural killer cells. T-lymphocytes, when cultured with irradiated Auto-Tu cells and low doses of rIL-2, showed an increased Auto-Tu lysis, while cytotoxicity against allogeneic tumor cells (including K562) was not observed. These data indicate that regional injection of rIL-2 can activate lymphokine-activated killer cells from LN lymphocytes but also induce and/or expand a T-cell population expressing a restricted Auto-Tu cytotoxicity.