TGF-beta1 is a pleiotropic cytokine, which prevents inappropriate autoimmune responses and balances the requirements of proper immune cell levels during pathologic states that trigger the immune response. We assessed the serum levels of TGF-beta1 and determined the relationship between TGF-beta1 and clinical parameters in patients with rheumatoid arthritis (RA) and Sjögren's syndrome (SS) secondary to RA (SS + RA). Comparison of the serum levels of TGF-beta1 in patients with RA, SS + RA and NHD differed significantly (51.7 +/- 12.4 ng/ml (RA); 33.0 +/- 3.1 ng/ml (SS + RA) and versus 31.6 +/- 2.0 ng/ml (NHD)). We further found correlations between TGF-beta1 levels and radiologically defined joint damage determined by the Steinbrocker scoring system, symptoms and signs of SS. We conclude that serum levels of TGF-beta1 may reflect ongoing autoimmune inflammation and correlate with joint damage in RA.