Circulating tenascin-C (TNC) is raised in rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), idiopathic inflammatory myositis (IIM), psoriatic arthritis (PSA) and ankylosing spondylitis (AS) patients but not in Sjogren's syndrome (SS) and TNC serum concentration increases with disease duration in RA. (A) TNC levels were determined by ELISA in serum samples from healthy controls (N) (n = 19), and patients with RA (n = 40), SLE (n = 24), IMM (n = 25), SS (n = 24), PSA (n = 6) or AS (n = 14). Each point represents the mean value of duplicate samples from an individual. Significant differences between patients and healthy controls were analysed by Mann-Whitney two-tailed analysis; ****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05, ns = not significant. (B) The RA cohorts were grouped according to disease duration into early (duration < 3 years) and late (duration > 3 years) RA. TNC levels from serum were determined by ELISA. Bars represent the mean plus standard error of the mean (SEM) from pooled data from 19 controls (N), 24 early RA or 16 late RA patients; *P < 0.05 (unpaired t-test).