Background It is unknown whether the association of anemia with elevated plasma levels of B-type and atrial natriuretic peptides (BNP and ANP) is mediated by the hemodynamic effects of anemia. Methods and Results The study group comprised 237 consecutive patients (BNP, median [interquartile range], 28.3 [9.5-77.1] pg/ml; ANP, 17.8 [8.5-39.0] pg/ml) undergoing determination of hemoglobin (Hb) and natriuretic peptide levels and cardiac catheterization for evaluation of coronary artery disease (CAD). Hb correlated with BNP (r=-0.36, p<0.001) and ANP (r=-0.35, p<0.001). Patients with anemia (Hb <12 g/dl for females; <13 g/dl for males, n=63) were more likely to be older with reduced body mass index and renal function, greater severity of CAD and to have higher heart rate, mean pulmonary capillary wedge pressure, and cardiac output. Anemia was a significant predictor for elevated (>third quartile value) natriuretic peptide levels and the predictive value remained significant after adjustment for other predictors, including increased left ventricular end-diastolic pressure and differences in clinical and hemodynamic variables between patients with and without anemia (adjusted odds ratio [95% confidence interval] for elevated BNP and ANP levels, 7.39 [2.76-19.8] and 2.56 [1.08-6.07], respectively). Conclusion Anemia is an independent predictor for elevated natriuretic peptide levels in patients with known or suspected CAD. (Circ J 2008; 72: 212 - 217)