Natural cell-mediated cytotoxicity (NCMC) was measured in 7 patients with Sjögren's syndrome without complication of connective tissue disease, 5 patients with Sjögren's syndrome associated with connective tissue disease other than rheumatoid arthritis (RA), 13 patients with Sjögren's associated with RA, and 29 patients with RA without Sjögren's. All 25 patients with Sjögren's syndrome showed a significantly suppressed NCMC. In the patients with RA but without Sjögren's, the NCMC for 21 female patients was rather enhanced when compared with controls, while 8 male patients did not differ from controls. The reduced NCMC in the Sjögren's patients did not seem to correlate with the presence of antilymphocyte antibody. A more accelerated rate of NCMC was demonstrated in the patients with RA who were receiving gold therapy.