The status of natural killer (NK) cell activity in peripheral blood, based on number and functional state, was studied in relation to the clinical and histopathologic stage of 52 patients with laryngeal carcinoma and in 23 healthy controls. The number of NK cells, estimated using CD16 and CD56 monoclonal antibodies, was similar in patients and controls and showed no relation to tumor size and nodal involvement. NK cell function did not show significant differences in spontaneous cytotoxic activity either overall or in relation to tumor size and the presence of palpable lymph nodes. However, cytotoxic activity was significantly lower in patients who had histologically confirmed nodal involvement. NK activity under 36% (the percentage of specific lysis at an effector:target dilution of 50:1) was suggested the probable presence of nodal metastases and was a highly sensitive and specific test. In patients with laryngeal carcinoma, NK-cell cytotoxic activity may be an independent prognostic parameter for evaluating cervical lymph node involvement.