In an attempt to clarify the mechanisms regulating the release of atrial natriuretic peptide (ANP) in man, ANP levels in pulmonary arterial plasma determined by RIA were correlated to hemodynamic variables in 17 patients with heart disease who underwent cardiac catheterization and angiocardiography. In addition, plasma ANP levels in various blood vessels were determined in 7 patients with heart disease and in 7 normal subjects to determine the source and the site of removal of circulating ANP. A significantly positive correlation was found between plasma ANP levels and mean pulmonary arterial wedge pressure, while the correlation between plasma ANP levels and mean right atrial pressure was not significant. After the injection of contrast medium, both mean right arterial pressure and plasma ANP levels increased, and a significant positive correlation was found between the two variables. When ANP levels in plasma collected from various blood vessels were compared, the highest levels were found in the coronary sinus. Plasma ANP levels in the renal vein were the lowest and were 50% of the levels in the aorta. Plasma ANP levels in the superior vena cava and internal jugular vein were higher than that in the antecubital vein. Analysis of immunoreactive ANP in pooled plasma by high performance liquid chromatography revealed that the retention time of the main ANP peak coincided with that of synthetic human alpha ANP. These results indicate that circulating ANP mainly originates from the heart, the kidney rapidly takes up a significant amount of ANP from the circulation, and an increase in both left and right atrial pressure triggers ANP release in man.