It is not clear whether brain natriuretic peptide (BNP) or N-terminal proBNP (NT-proBNP) is superior as a diagnostic and prognostic indicator in cardiac diseases. Here, we compare the clinical correlations of both peptides in a population of 92 ambulatory patients with heart failure, using a well-established immunoradiometric assay (IRMA) for BNP and an automated electrochemiluminescence immunoassay for NT-proBNP. The analytical correlation between the two peptides was satisfactory over a wide range of concentrations (1-686 pM for BNP) with the equation: NT-proBNP = 3.48 x BNP -19 and a correlation coefficient r2=0.94. In addition, the concentration of both peptides increased in a similar fashion according to the severity of the disease New York Heart Association (NYHA) functional class, left ventricular ejection fraction, etiology) and age; for instance, the ratios between median levels measured in NYHA class III vs. class II patients were comparable for BNP (383 vs. 16 pM, ratio 24) and NT-proBNP (1306 vs. 57 pM, ratio 23). We conclude that N-terminal proBNP, as assayed in the present study, correlates equally to BNP with clinical variables in patients with heart failure.