The role of the fibrinolytic enzyme system in inflammatory joint disease has been addressed by several experimental approaches. In our study we examined synovial fluid (SF) in several different diseases for alpha 2-plasmin inhibitor-plasmin complexes by an enzyme linked immunosorbent assay (ELISA). These complexes are present in both rheumatoid and nonrheumatoid SF, with highest levels seen in septic arthritis. Thus the plasminogen system is intact in inflammatory SF, and plasmin may play a role in the local inflammatory process.