Objective: To investigate the changes in B-type natriuretic peptide concentrations in patients with severe sepsis and septic shock and to investigate the value of B-type natriuretic peptide in predicting intensive care unit outcomes. Design: Prospective observational study. Setting. General intensive care unit. Patients: Forty patients with severe sepsis or septic shock. Interventions. None. Measurements and Main Results: B-type natriuretic peptide measurements and echocardiography were carried out daily for 10 consecutive days. In-hospital mortality and length of stay were recorded. The admission B-type natriuretic peptide concentrations were generally increased (747 +/- 860 pg/mL). B-type natriuretic peptide levels were elevated in patients with normal left ventricular systolic function (568 +/- 811 pg/mL), with sepsis-related reversible cardiac dysfunction (630 +/- 726 pg/mL), and with chronic cardiac dysfunction (1311 +/- 1097 pg/mL). There were no significance changes in B-type natriuretic peptide levels over the 10-day period. The daily B-type natriuretic peptide concentrations for the first 3 days neither predicted in-hospital mortality nor correlated with length of intensive care unit or hospital stay. Conclusion: B-type natriuretic peptide concentrations were increased in patients with severe sepsis or septic shock regardless of the presence or absence of cardiac dysfunction. Neither the B-type natriuretic peptide levels for the first 3 days nor the daily changes in B-type natriuretic peptide provided prognostic value for in-hospital mortality and length of stay in this mixed group of patients, which included patients with chronic cardiac dysfunction.