Functions of peripheral blood lymphocytes and neutrophils from 30 oral lichen planus (OLP) patients were examined using healthy persons as controls. Two-color flow cytometry of lymphocytes revealed no proportional difference in CD3 or CD4 cells between OLP and controls. CD8CD11b (suppressor T) and CD3HLA-DR+ cell populations increased significantly in OLP when compared with controls, and CD4/CD8 cell ratio decreased in OLP. Mitogenic response of patients' CD8 and CD4Leu8- cells was similar to that in controls. However, weaker blastogenesis of CD4Leu8+ cells, the most excellent responders in T cell subsets, was observed in OLP. Serum IFN beta level in OLP (8.4 +/- 4.8 IU/ml) was significantly lower than in controls (13.7 +/- 5.0 IU/ml) whereas no difference between the two groups could be found in IFN alpha or gamma. As for in vitro cytokine production by IL-2-stimulated lymphocytes, there was no difference in GM-CSF generation between the two groups, but, IFN gamma and IL1 beta production of patients' lymphocytes was less than that in healthy donors (57.6 +/- 50.7 VS 78.7 +/- 39.6 u/ml, 152.3 +/- 93.5 VS 258.7 +/- 65.4 pg/ml, respectively). Moreover, superoxide generation of patients' neutrophils by PMA stimulation was significantly insufficient as compared with controls' (84.9 +/- 30.9 VS 110.8 +/- 24.1 pmol/min/10(4) cells). Nevertheless, natural killer cell activities of both groups distributed in the same range. These results suggest that OLP patients' lymphocyte and neutrophil functions are impaired, and that cellular immunosuppression is a pathologic characteristic of OLP.