The value of natriuretic peptides, both B-type natriuretic peptide (BNP) and N-terminal prohormone brain natriuretic peptide (NTproBNP), for determining diagnosis, severity, and prognosis of emergency department (ED) patients with acute decompensated heart failure (ADHF) has been well documented. Emerging data support the hypothesis that repeated natriuretic peptide determinations in the acute phase of ADHF may assist in confirming the diagnosis, monitoring drug therapy, and evaluating the adequacy of patient stabilization. Data from the authors' group demonstrate that in patients admitted to the ED for acute dyspnea, serial NTproBNP measurement at admission and 4, 12, and 24 hours later was useful in confirming the diagnosis of ADHF compared with patients with chronic obstructive pulmonary disease. Moreover, in the same patients receiving intensive intravenous diuretic therapy, there was a progressive reduction of NTproBNP blood levels from hospitalization to discharge (P<.001), accompanied by clinical improvement and stabilization of heart failure. More recently, the authors also demonstrated that in ADHF patients improving with diuretics, a progressive reduction in BNP levels was observed, starting 24 hours after ED admission and continuing until discharge. Comparing BNP and NTproBNP, there was a significant correlation between NTproBNP and BNP levels but not between NTproBNP's and BNP's percent variation compared with baseline. In ADHF, serial ED measurements of BNP are useful for monitoring the effects of treatment. A reduction in BNP from admission to discharge is indicative of clinical improvement.