The effects of synthetic human atrial natriuretic peptide (hANP) on arterial blood pressure, heart rate, and renal functions were evaluated in conscious trained dogs in moderate sustained water diuresis. Synthetic hANP was given i.v. over 3 min at doses of 0.27-2.16 micrograms kg-1 body wt. It did not cause significant changes in blood pressure or heart rate. The rate of sodium excretion increased 20-fold following 2.16 micrograms kg-1 and 2.5-fold after 0.54 micrograms kg-1. Natriuresis was immediate and vanished after 10 min, regardless of dose. The concomitant increase in diuresis was less than 50%, but significant for a longer period of time. Increases in potassium excretion were significant, but small, that is, by a factor of 1.5-2.8. All natriuretic doses of hANP increased PAH clearance (at constant blood pressure), but some did so without measurably affecting creatinine clearance.