This study is, to our knowledge, the first attempt to evaluate cellular immune mechanisms in regional lymph nodes of patients with head and neck cancer. Twenty lymph nodes from eight patients with stage III-IV squamous cell carcinoma were evaluated using an in vitro culture system. The T-cell mitogenic (concanavalin A) response of patients' peripheral blood mononuclear cells was modulated by the addition of cells from regional lymph nodes removed at neck dissection. Modulatory activity showing augmentation was significantly correlated with the size of the primary tumor and histopathologic grade of the tumor. Modulatory activity did not correlate with the histologic pattern of lymph node reactivity. Although these relationships suggest that regional immunity may be important in tumor-host interactions, further study is necessary to establish their biologic and prognostic importance.