In rheumatoid arthritis (RA) an immuno dysregulation alters the release of neopterin from human monocytes/macrophages, probably by activation of a feed-back regulation mechanism in pterin metabolism. With the overactivation of T-lymphocytes, the secretion of interleukin-2 and its receptor (IL-2R) is influenced. Investigation on 84 RA patients has shown that this immunoactivation is accompanied by an increased secretion of neopterin and soluble IL-2R in the serum, and that both parameters are very suitable for detection of inflammatory disease activity. The significant correlation between neopterin and IL-2R (r = 0.65; p < or = 0.001) in RA points out a possible connection in pathomechanisms of the immune system.