Background Hepatocyte growth factor (HGF) has been reported as a marker of atherosclerosis and of thrombi synthesis, but the relationship between HGF and proven coronary thrombi has not been described. The aim of this study was to investigate this relationship in patients with chest pain. Methods and Results The study group comprised 107 patients with chest pain (61 acute myocardial infarction (AMI), 18 unstable angina, 15 stable angina, and 13 others; 65 males, 42 females; 66±11 years old). The presence of thrombi was evaluated by angiography, intravascular ultrasonography, angioscopy, and computed tomography. Serum HGF concentrations were measured using a new enzyme-linked immunosorbent assay. Serum HGF was significantly higher in the patients with AMI (335.0 ±197.5 pg/ml), unstable angina (269.1±152.7 pg/ml), acute aortic dissection (320.3±116.5 pg/ml), and pulmonary thromboembolism (292.5±101.9 pg/ml), than in those with stable angina (171.2±56.1 pg/ml). Serum HGF concentration was also higher in those patients with proven thrombi than in those patients without (326.7±189.7 pg/ml vs 226.9±110.8 pg/ml). Conclusion Increased serum HGF concentrations correlate with the presence of thrombi in patients with acute coronary syndrome, acute aortic dissection, and pulmonary thromboembolism. (Circ J 2004; 68: 645 - 649)