Macrophages are normal constituents of synovial tissue, and in inflammatory synovitis the number of synovial macrophages increases. Synovial macrophages and their secretory products are important in initiating, propagating, and maintaining the synovial inflammation in rheumatoid arthritis (RA). The purpose of this study was to determine the absolute numbers of macrophages in synovia resected from patients with RA and osteoarthritis (OA) and to determine their abilities to produce and/or functionally express tumor necrosis factor (TNF), interleukin-1 (IL-1), and tissue factor (thromboplastin). Results demonstrate that synovial tissue from RA patients (as compared to that from OA patients) weighed more, contained more cells, more macrophages, and more multinucleated giant cells (macrophage polykaryons). Also, isolated cells from both OA and RA patients had tissue factor activity and could produce TNF and IL-1 with in vitro culture, but these parameters were not different in cells from OA and RA patients. RA patients receiving glucocorticoid treatment for their arthritis had fewer total synovial cells than did patients not on glucocorticoids, but treatment with nonsteroidal anti-inflammatory agents did not alter cell numbers. Patient treatment with glucocorticoids or non-steroidal anti-inflammatory drugs did not influence the ability of their isolated cells to produce TNF or IL-1.