BACKGROUND Immunosuppression in patients with head and neck cancer is well recognized. Previous investigations have demonstrated graded immunosuppression that becomes more pronounced as lymphocyte activity is measured closer to the primary neoplasm. In fresh tumors, a soluble factor has been identified that may partly account for the observed graded immunosuppression. OBJECTIVE To examine the effect of soluble factors produced by head and neck sqamous cell carcinoma cell lines on the generation of lymphokine activated killer cell cytotoxicity and peripheral blood lymphocyte proliferation induced by interleukin 2, concanavalin A, and phytohemagglutinin. METHODS Conditioned supernatant fluids were generated in a 4-day incubation period, using 5 head and neck squamous cell carcinoma cell lines, and were assayed for the ability to inhibit the generation of lymphokine activated killer cell cytotoxicity and naive peripheral blood lymphocyte proliferation induced by interleukin 2, concanavalin A, and phytohemagglutinin. RESULTS All conditioned supernatant fluids significantly inhibited the generation of lymphokine activated killer cell cytotoxicity relative to controls, and this inhibition was dose dependent. In contrast, supernatant fluids from a myelogenous leukemic tumor cell line, K562, and an ovarian epithelial cell line, SKOV-3, failed to inhibit cytotoxicity. Supernatant fluids conditioned with head and neck squamous cell carcinoma cell lines also profoundly inhibited the naive peripheral blood lymphocyte proliferation induced by interleukin 2, concanavalin A, and phytohemagglutinin. CONCLUSIONS These studies demonstrate that the cell lines of head and neck squamous cell carcinoma produce soluble factors that inhibit lymphocyte function. Furthermore, these experiments suggest that the inhibition previously observed with enzymatically disaggregated fresh tumors is due to factors produced by the tumor cells rather than by other cells within the tumor matrix.