1. Saline infusion produced concurrent mean increases over basal in plasma and urinary atrial natriuretic peptide (ANP) of approximately 100%. 2. Subpressor calcium infusion also produced concurrent increases in plasma and urinary ANP of 38 and 60% respectively. 3. Urinary ANP appeared to be as responsive to the dynamic stimulation of saline and calcium infusion as plasma levels. 4. Urinary ANP may be useful when an integrated estimation of ANP secretion and metabolism is required. Further studies are required to assess clinical utility in a variety of settings, for example during endopeptidase 3.4.24.11 inhibition.