Increments in circulating thrombomodulin levels reflect endothelial cell injury. Thrombomodulin can also be synthesized by several inflammatory cells including monocytes, neutrophils, and thrombomodulin itself can modulate the inflammatory response. In this study, we assessed circulating thrombomodulin concentrations in patients with familial Mediterranean fever (FMF). Twenty-five patients with FMF (F/M: 14/11) (mean age: 31.1 +/- 9.7 years) and 25 healthy controls (F/M: 13/12) (mean age: 34.6 +/- 7.0 years) were involved in the study. Thrombomodulin levels were measured by commercially available enzyme-linked immunosorbant assay (ELISA) (Immunoassay of thrombomodulin Diagnostica Stago, Asnieres-Sur-Seine, France). Twenty of the patients were in attack-free period and the remaining five had been during acute FMF attacks. Thrombomodulin levels were higher in the study group (20.9 +/- 12.1 ng/ml) than healthy controls (14.1 +/- 8.4 ng/ml) (p < 0.05). Circulating thrombomodulin levels were also higher in attack-free FMF patients (22.4 +/- 12.9 ng/ml) than controls. This study disclosed for the first time significantly higher increments in the circulating levels of thrombomodulin in FMF. This observation could be a consequence of injured endothelium and/or activated inflammatory cells.