The tumor-polymorphonuclear neutrophil (PMN) relationship can be altered by the release of toxic molecules, such as nitric oxide (NO). The aim of the present study was to examine the expression of the inducible synthase of NO (iNOS) and NO production by human neutrophils of patients with oral cavity cancer. For comparison we performed similar examinations in autologous peripheral blood mononuclear cells (PBMCs). PMNs and PBMCs were isolated from the whole blood of 27 patients with squamous cell carcinoma of the oral cavity. iNOS protein expression in these cells was detected by Western blot. Total nitrite as an indicator of NO concentrations in the culture supernatants and the serum of patients was measured using a colorimetric assay. The PMNs of oral cavity cancer patients showed a significantly lower intensity of iNOS expression than those of healthy controls. The PBMCs of patients showed a more intensive expression of iNOS than the PMNs, but a lower intensity than the PBMCs of the controls. The expression of iNOS in rhIL-6 and rhIL-15-stimulated PMNs and PBMCs of patients increased in comparison with unstimulated cells. We observed lower productions of NO by PMNs and PBMCs of patients than those of the control group. The results revealed that altered iNOS expression and NO production are more characteristic of PMNs than of PBMCs of patients with oral cavity cancer. Additionally, this study provided new information about IL-6 and IL-15 activity in a tumor-bearing host.