We measured soluble interleukin-2 receptors (sIL-2R) in plasma and/or joint fluid (JF) from patients with rheumatoid arthritis (RA: 16 patients), Sjögren's syndrome (SS: 24 patients) and Behçet's disease (BD: 23 patients). Plasma sIL-2R levels were significantly higher in RA patients (956 +/- 994 U/ml, p < 0.01) and SS patients (1025 +/- 1112 U/ml, p < 0.01) than 20 healthy subjects (338 +/- 159 U/ml), but not significantly increased in BD patients (408 +/- 329 U/ml). sIL-2R levels higher than the mean of healthy subjects +2 standard deviations were observed in 3 BD patients (13.0%), 7 RA patients (43.8%) and 10 SS patients (41.7%). sIL-2R levels positively correlated with erythrocyte sedimentation rates and C-reactive protein levels in RA patients, or IgM levels in SS. There was no significant correlation between plasma sIL-2R levels and disease activity, clinical symptoms, or other laboratory parameters in BD patients. However, sIL-2R concentrations in the JF from 4 BD patients (1644 +/- 198 U/ml: p < 0.05) or 16 RA patients (3946 +/- 5424 U/ml: p < 0.01) were significantly higher than corresponding plasma sIL-2R concentrations. Above results indicate that lymphocytes are being activated in patients with RA or SS and in the inflammatory lesions of BD patients, while the whole immunologic activation are relatively lower in BD than RA and SS.