Cytofluorometric analysis was performed to characterize the surface phenotype and activation status of freshly isolated synovial tissue lymphocytes (STL) and peripheral blood lymphocytes (PBL) from 7 patients with rheumatoid arthritis (RA). Proliferative synovium was enzymatically digested to obtain tissue-derived lymphocytes. Indirect immunofluorescent staining of patient PBL and STL with a variety of monoclonal antibodies failed to reveal a consistent alteration in the number of CD4+ (helper/inducer) PBL or STL. However, there was a significant decrease in the number of CD8+ (suppressor/cytotoxic) cells in rheumatoid STL (P less than 0.05). A significant reduction in the density of the T cell differentiation antigens CD3 and CD4 was observed in RA PBL and STL, compared with control PBL. These differences in antigen density were not seen when normal PBL were subjected to the same enzymatic digestion. Both RA PBL and STL manifested increased expression of HLA-DR antigens, without augmentation of interleukin-2 receptor expression. Alterations in the expression of the T cell differentiation antigens and activation antigens by patient PBL closely paralleled the abnormalities observed in STL. In contrast, STL of patients with RA exhibited an increase in the expression of the adhesion-related glycoproteins (leukocyte function-associated 1 [LFA-1] and very late activation 1 [VLA-1] antigens), not observed with autologous PBL. These studies demonstrate that lymphocytes isolated from the synovial tissues of RA patients bear an activated phenotype, exemplified by the modulation of CD3 and CD4 and the expression of HLA-DR.(ABSTRACT TRUNCATED AT 250 WORDS)