In vitro analysis of polymorphonuclear neutrophils (PMN) has allowed various stages of cell activation to be distinguished, characterized by the expression level of specific membrane markers and of functional receptors. Among those, TNF-alpha receptors (TNF-R) are modulated by various PMN activators, a mechanism which may be important to control cell responses to TNF in inflammatory reactions such as rheumatoid arthritis (RA). PMN, isolated from the blood of 36 RA patients and from the synovial fluid of 23 of them, were analysed for membrane expression of the two TNF-R (p55 and p75). Soluble p55 and p75 (sTNF-R) and TNF concentrations were measured in the plasma and synovial fluid by specific ELISA assays. Our results show that PMN from the blood of RA patients bear a normal number of TNF-R, with a normal p55/p75 ratio, compared with PMN from normal controls. Soluble TNF-R levels were similar in patients and normal plasma. In spite of high endogenous TNF concentration, patients' circulating PMN were not activated, as shown by a CD11b/CD18 expression similar to that of control resting cells. In contrast with blood neutrophils, PMN from RA patients' synovial fluids had an activated phenotype, characterized by increased expression of CD11b, decreased expression of leukosialin, CD43, and the appearance on the plasma membrane of an azurophil granule protein, CD63. High levels of soluble TNF-R were measured in RA synovial fluids. Nevertheless, membrane TNF-R levels and p55 and p75 proportions were similar to those of PMN from normal blood. These results suggest the existence of regulatory mechanisms which maintain a stable neutrophil expression of TNF-R as well as a balance between both types of receptors in inflammatory situations where neutrophils are strongly activated.