Plasma levels of C-reactive protein (CRP) and serum amyloid A protein (SAA), inflammatory markers, and soluble thrombomodulin (s-TM), a marker of endothelial damage. are thought to be related to coronary artery disease. However, the relationship between these inflammatory markers and endothelial injury in atherosclerotic coronary arteries is still unclear. Fifty-five patients who underwent coronary angiography were classified into 3 groups according to the severity of left coronary arterial atherosclerosis evaluated by the Gensini score (GS; normal: score = 0, n = 15; mild: 0 < score < 15, n = 29; severe: score > or = 15, n = 11). Blood samples were obtained from the aortic root (Ao) and coronary sinus (CS) and plasma CRP and SAA levels were measured by latex turbidimetric immunoassays, and s-TM levels were determined by an enzyme-linked immunosorbent assay. The difference between marker concentrations in the Ao and CS of the coronary circulation was expressed as the coronary sino-arterial (CS-Ao) difference. The CS-Ao differences of s-TM and SAA were significantly higher in patients with severe atherosclerosis than in normal patients (P < 0.01), and showed weak but significant positive correlations with the GS (r = 0.34, P < 0.01 and r = 0.33, P < 0.05, respectively). The CS-Ao differences in CRP did not differ among the three groups, and did not correlate with the GS. The results of our study reveal a possible relationship between endothelial cell injury and inflammation in atherosclerotic coronary arteries.