The mechanisms involved in the diuretic action of the recently discovered group of atrial natriuretic peptides (ANP) are not entirely clear. To determine whether the diuresis and the changes in blood pressure produced by alpha-human ANP (alpha-hANP) involved a concomitant modification of circulating arginine-vasopressin (arg-VP), we evaluated the effects of synthetic alpha-hANP on plasma alpha-hANP, arg-VP, electrolytes, protein, haematocrit, blood pressure and urinary sodium and water excretion in 10 normal subjects on daily sodium intakes of 16, 140 and 310 mmol, respectively. Plasma alpha-hANP levels before and during a 45-min alpha-hANP infusion (0.09 micrograms/kg per min) tended to be slightly, though not significantly, higher on 'normal' or high sodium intake than on low sodium intake. Alpha-human ANP produced a fall in diastolic blood pressure (P less than 0.001) and to a lesser extent mean blood pressure, and a rise in heart rate (P less than 0.001) at all levels of sodium intake. The induction of diuresis, natriuresis and plasma volume contraction caused by alpha-hANP was greater on a high sodium intake than on 'normal' or low sodium intakes (P less than 0.001). Plasma arg-VP concentrations were lower (P less than 0.05) on a high than on a low sodium intake, but were not altered by an alpha-hANP infusion. The data indicate that in healthy humans circulating arg-VP may tend to decrease in response to a high salt diet. However, marked changes in plasma alpha-hANP concentrations have, regardless of sodium intake, no relevant influence on circulating arg-VP.(ABSTRACT TRUNCATED AT 250 WORDS)