OBJECTIVE Recent evidence suggests the presence of a dual natriuretic peptide system consisting of atrial natriuretic factor (ANF) from the atrium and brain natriuretic peptide (BNP) from the ventricle. Discrete roles have been postulated for these two natriuretic peptides in the control of circulatory homeostasis. We have therefore compared the release of ANF and BNP in response to an acute saline load to explore a differential pattern of release for the two natriuretic peptides in man. METHODS The effects of an acute saline infusion on plasma ANF and BNP concentrations were studied in 10 normal male volunteers. METHODS Subjects were studied on two study days in the semirecumbent position. An acute intravenous saline infusion (250 ml/min) of 18 ml/kg isotonic sodium chloride-potassium chloride solution was administered on one of the two study days. No infusion was administered on the other day as a control. RESULTS Plasma ANF concentrations increased significantly (P < 0.01) with saline loading without any detectable changes in plasma BNP concentrations up to 60 min following infusion. Heart rate and systolic and diastolic blood pressure were unchanged after saline loading. CONCLUSIONS We have shown that an acute intravenous saline load causes an increase in plasma ANF concentrations with no detectable increase in plasma BNP at least up to 60 min after the acute saline load in man. These results support the view that the release of ANF and BNP may be regulated differently, especially with regard to the time required for the acute release of each peptide.