Biologically active B-type natriuretic peptide or brain natriuretic peptide (BNP) and biologically inactive N-terminal proBNP (NT-proBNP) are secreted into the bloodstream by the heart and provide primarily information regarding the filling pressures in the heart. The accuracy of plasma BNP levels in the diagnosis of heart failure is comparable to that of plasma NT-proBNP levels. Reliable assays have been developed for both peptides, some of which can be used for rapid diagnosis in the emergency clinic. In both groups of patients with heart failure and the general population, there is a relationship between the plasma BNP and NT-proBNP levels and the risk of cardiovascular death, after correction for the traditional risk factors. Screening studies using the determination of BNP or NT-proBNP levels in order to detect patients with heart failure at an early stage cannot be recommended because their specificity is too low: in addition to heart failure, the plasma BNP or NT-proBNP level is affected by age, gender, body mass index, renal function, and pulmonary capacity. There are indications that the introduction ofa rapid BNP determination for patients that present to the emergency clinic with acute dyspnoea will lead to more effective diagnosis and treatment. Sequential determinations ofthe plasma BNP or NT-proBNP levels in inpatients and outpatients with heart failure can help to optimise the treatment, thus decreasing the morbidity and mortality that are associated with heart failure.