Neurohumoral systems activated in heart failure are reviewed in relation to prognostic and diagnostic information. Plasma levels of noradrenaline, renin, vasopressin, endothelin-1, ANP, BNP, and TNF-α are all elevated in heart failure. Most of these factors correlate with the prognosis, but only a minor part seems to posses additional, independent information when other information that is normally available in such patients is taken into account. At present, the diagnosis of heart failure cannot be made on only one blood sample. However, neuroendocrine markers seem: 1) to have a role in the diagnosis and classification of heart failure, 2) to be useful in providing a 'neuroendocrine profile', which elucidates different aspects of heart failure, and 3) to be of probable value in the choice and titration of medical treatment for the individual patient in the future.