Background Adiponectin, which is a collagen-like plasma protein produced by adipose tissue, has anti-atherogenic and anti-inflammatory effects. Plasma adiponectin levels in patients with congestive heart failure (CHF) were determined, as well as relationships between the plasma levels of adiponectin and other hormones. Methods and Results The study group comprised 90 patients with CHF and 20 control subjects, who were divided into 4 subgroups according to New York Heart Association (NYHA) functional class. Plasma levels of adiponectin, tumor necrosis factor (TNF)-α and brain natriuretic peptide (BNP) and cardiac hemodynamics were determined. Plasma adiponectin levels were significantly increased according to the severity of NYHA class in the patients with CHF; control: 6.2±1.0; NYHA I: 8.5±1.9, NYHA II: 12.0±2.2, NYHA III: 13.0±2.7, NYHA IV: 14.9±2.7 μg/ml (p=0.0008). Similarly, plasma BNP levels were significantly increased in accordance with the NYHA class. Plasma adiponectin levels correlated positively with BNP (r=0.40, p=0.0002) and TNF-α (r=0.49, p=0.0001), and correlated negatively with cardiac index (r=-0.27, p=0.05). In 24 of 46 patients in the NYHA III and IV subgroups, according to the prompt improvement in cardiac function, levels of both plasma adiponectin and BNP were significantly reduced (p<0.0001). Conclusion Plasma adiponectin levels increased according to the severity of CHF and, moreover, they correlated with the plasma levels of BNP and TNF-α. These results indicate that augmented release of adiponectin is involved in the pathogenesis of CHF and further study is needed to elucidate its exact role. (Circ J 2006; 70: 1557 - 1562)