T cells bearing gamma/delta T cell receptor (gamma/delta + T cells) and their expression of activation antigen (HLA-DR) or the marker of natural killer (NK) cells (CD56), were examined in the peripheral blood lymphocytes (PBL) from twenty-two patients with Sjögren's syndrome (SS) by three-color flowcytometry to elucidate possible pathological roles of the T cell subset in SS. The frequency of gamma/delta + T cells in PBL was not elevated in SS patients, while that of gamma/delta - T cells, which are T cells bearing the alpha/beta T cell receptor (alpha/beta + T cells), was significantly low in the patients, as compared with 22 healthy controls. We found that the proportions of activated cells (HLA-DR+) in both the gamma/delta + and alpha/beta+T cell subsets were significantly higher in the patients than in the controls. The proportions of HLA-DR+ cells in cells in both patients and controls. Furthermore, the frequency of activated cells in both T cell subsets correlated with the duration of disease in SS patients. However, no difference was found in the percentages of total CD56+ cells, CD56+CD3- cells (true NK cells), CD56+CD3+T cells, CD56+gamma/delta+T cells, or CD56-gamma/delta+T cells between the patients and controls. The above results indicate that immunologic activation in SS patients is progressive and involves both alpha/beta+ and gamma/delta+ T cell subsets.