Reduced natural killer (NK) cell activity of peripheral blood lymphocytes (PBL) has been reported in a number of diseases including Sjögren's syndrome (SS). In this study, we used 2 monoclonal antibodies directed toward NK cells (anti-Leu-7 and anti-Leu-11) for determining NK cell activity in 29 patients with SS (9 with primary SS and 20 with secondary SS). The NK activity of PBL was simultaneously determined by the 51Cr release method using K562 as target cells. Contrary to previous reports, we did not find reduced NK activity of PBL in our patients compared with sex- and age-matched healthy controls. Although the percentage of Leu-7+ cells was significantly higher in the patients than in the controls (P less than 0.05), the absolute number of circulating Leu-7+ cells was not different between the groups. The percentage of Leu-11+ cells, however, was not significantly different between the patients and the controls, but the number of circulating Leu-11+ cells was significantly fewer in the patients than in the controls (P less than 0.05). Between the primary and secondary SS groups, no significant differences were found in NK cell activity or in the percentage of Leu-7+ or Leu-11+ cells. Furthermore, we found a significant correlation of NK activity with the percentage of Leu-11+ cells (P less than 0.05) in the controls as well as the SS patients, although a significant correlation was not identified between NK activity and the percentage of Leu-7+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)