The activity of plasminogen activators and inhibitors in the synovial fluid and plasma of patients with various forms of chronic arthritis was characterised. Tissue-type plasminogen activator antigen (t-PA:Ag), urokinase-type plasminogen activator antigen (u-PA:Ag), the proenzyme single chain u-PA (scu-PA), and plasminogen activator inhibitor (PAI) were measured in the synovial fluid and plasma of 22 patients with seropositive rheumatoid arthritis (RA), 13 with seronegative RA, and 23 patients with various forms of arthritis. In all patient groups the levels of t-PA:Ag in synovial fluid were lower and the levels of u-PA:Ag and PAI higher than plasma levels. Synovial fluid u-PA was more activated than plasma u-PA. Comparison of the patient groups showed that the largest differences between fibrinolytic parameters in synovial fluid and plasma were present in patients with seropositive RA followed by patients with seronegative RA and patients with various forms of arthritis. This order paralleled the functional and radiological scores of joint destruction in the patient groups studied. The results of this study indicate that suppression of t-PA production and enhancement of u-PA synthesis and activation in arthritic joints are associated with the clinical severity of arthritis.