In 15 patients suffering from systemic sclerosis (PSS) the function of CD8+ circulating lymphocytes was assayed by determining soluble CD8 antigen (sCD8) both in sera and in 48 hr PHA-conditioned media of peripheral blood mononuclear cells (PBMCs). Furthermore, the frequency of circulating activated CD8+ cells, which express DR antigens, interleukin-2 receptor, and transferrin-receptor, was determined by cytofluorographic analysis. The results of this preliminary study indicate that only in 6 PSS sera sCD8 was elevated as compared to healthy controls; furthermore, we found slightly increased sCD8 in culture media from PSS patients. The frequency of circulating activated CD8+ cells was similar both in PSS patients and in controls. Overall, our findings suggest that CD8+ cell activation is not a major phenomenon in PSS.