&NA;Synthetic atrial natriuretic factor (ANF) was either added to suffusate solutions (30 nM) or infused into the jugular vein (0.1 nanomol/min/100 g) of anesthetized rats. Steady‐state blood flow was calculated from arteriolar diameter and red blood cell velocity measurements using video microscopy in the intestinal or skeletal muscle microcirculation. Arterioles demonstrated spontaneous vasomotor tone by dilating to topical adenosine, but topical or intravenous ANF did not cause vasodilation. Either angiotensin, norepinephrine, or vasopressin was added to the suffusates in the presence or absence of a cyclooxygenase inhibitor (30 μM, meclofenamate or indomethacin) because each agonist is known to stimulate vasoactive prostanoid synthesis. In the intestine, angiotensin (500 nM) caused 40 ± 2% blood flow decreases during intravenous saline but only 23 ± 6% during intravenous ANF. Angiotensin (162 nM) and a cyclooxygenase inhibitor caused 19 ± 4% blood flow decreases but only 8 ± 5% decreases with cyclooxygenase inhibitor and topical ANF. In contrast, norepinephrine (2‐5 μM) caused vasoconstriction that was not altered by topical or intravenous ANF, either aione or in combination with cyclooxygenase inhibitors. In the spinotrapezius muscle, angiotensin (1‐2 nM) plus a cyclooxygenase inhibitor caused 40‐60% blood flow decreases but only 20‐30% decreases during intravenous or topical ANF. Topical or intravenous ANF did not alter the vasoconstriction evoked by arginine vasopressin (0.5‐1.0 nM) or by norepinephrine (40‐230 nM). Thus, 1) supraphysiologic concentrations of ANF produced no direct vasodilation in the intestinal or skeletal muscle microcirculation; 2) there was a regional difference in sensitivity to topically‐applied vasoconstrictor hormones between the two tissues; 3) ANF reduced, but did not eliminate, the vasoconstriction caused by angiotensin by a mechanism that did not involve cyclooxygenase products; and 4) ANF did not alter the vasoconstriction caused by norepinephrine or arginine vasopressin. (Circulation Research1987;61:42‐49)