To compare release of immunoreactive atrial natriuretic peptides (iANP) caused by distention of the right and left atria, dogs were prepared with occluding cuffs around either the ascending aorta (n = 5) or the pulmonary artery (n = 4). Graded inflation of the ascending aortic cuff for 60 min caused increments in left atrial pressure (LAP) but no change or a decrease in right atrial pressure (RAP). Plasma iANP increased significantly (P less than 0.01) in response to increases in LAP as small as 2.9 +/- 0.4 mmHg. There was a significant correlation between the increment in LAP and the rise in plasma iANP (r = 0.64, n = 25, P less than 0.01). Graded inflation of the pulmonary artery cuff caused increments in RAP and a fall in LAP. Plasma iANP increased significantly (P less than 0.01) in response to increases in RAP as small as 2.8 +/- 1.1 mmHg. Also, there was a significant correlation between the increments in RAP and the rise in plasma iANP (r = 0.69, n = 20, P less than 0.01). These results indicate that physiologic increases in either RAP or LAP is sufficient to cause increased plasma levels of iANP in conscious dogs.