This study is designed to aid in the evaluation of clinical disease activity in patients with idiopathic inflammatory myopathies, a diverse group of diseases that includes inflammation in skeletal muscle. Since the pathology includes primary muscle capillary endothelial cell damage, we have assessed markers of activation and injury to endothelial cells and activation of coagulation factors, including complexes of thrombin-anti- thrombin, plasmin-anti-plasmin, tPa, and thrombomodulin. We have studied 38 patients and are currently analyzing the data to determine clinical correlations with disease activity. A subset of patient shows an increase in thrombin-anti-thrombin complexes, which is a sensitive assay for activation of coagulation factors.