B-type natriuretic peptide (BNP), a neurohormone synthesized in the cardiac ventricles, is released as preproBNP and then enzymatically cleaved to the N-terminal-proBNP (NT-proBNP) and BNP upon ventricular myocyte stretch. Blood measurements of BNP and NT-proBNP have been used to identify patients with congestive heart failure (CHF). Important considerations for these tests include their half-lives in plasma, dependence on renal function for clearance, and the interpretation of their units of measure. The BNP assay currently available in North American markets, approved for use as a diagnostic aid in CHF and a prognostic marker in acute coronary syndromes (ACS), has particular advantages because it is available at the point of care and has had considerable use in clinical studies. In general, a BNP level less than 100 pg/mL has strong negative predictive value for CHF. In addition, BNP levels can be used to gauge the effect of short-term treatment of acutely decompensated CHF. BNP has been shown to be a reliable and independent predictor of sudden cardiac death. In the absence of renal dysfunction, NT-proBNP has also been shown to be of diagnostic value in CHF, related to CHF severity, predictive of sudden death, and prognostic for death in ACS. This article reviews the literature concerning the use of these peptides in a variety of clinical scenarios.