1. We studied plasma atrial natriuretic peptide (ANP) concentrations in seven normal subjects after the acute intravenous infusion of sodium chloride/potassium chloride solution (saline).
2. Three separate infusions of 6, 12 and 18 ml of saline/kg body weight each significantly increased the circulating concentration of ANP without changes of plasma osmolality or electrolyte concentrations.
3. The mean maximal rise of the plasma ANP concentration after the three saline infusions was significantly correlated (r = 0.74, P < 0.001) with, but occurred 10–30 min later than, the maximal atrial pressure rise.
4. These observations are in accord with the hypotheses that: (a) ANP is a circulating natriuretic factor; (b) atrial distension is an important stimulus to ANP release in man.