Background: B-type natriuretic peptide (BNP 1-32) plays an important physiologic role in cardiorenal homeostasis. Recently, it has been reported that BNP 1-32 is rapidly cleaved by the ubiquitous enzyme dipeptidyl peptidase IV to BNP 3-32, which lacks the two N-terminal amino acids of BNP 1-32. The bioactivity of BNP 3-32 in cardiorenal regulation is unknown. We hypothesized that BNP 3-32 has reduced vasodilating and natriuretic bioactivity as compared to BNP 1-32 in vivo. Methods and Results: Synthetic human BNP 3-32 and BNP 1-32 were administered to eight anesthetized normal canines. After baseline measurements, BNP 1-32 at 30 ng/kg/min was administered, followed by a washout, a post-infusion clearance, and a clearance with an equimolar dose of BNP 3-32. In four studies the sequence of BNP 1-32 and BNP 3-32 infusion was reversed. Peptides were compared by analyzing the changes from the respective preinfusion clearance to the respective infusion clearance. *p<0.05 between peptides. BNP 3-32 unlike BNP 1-32 did not decrease mean arterial pressure (0±1 vs. -7±2* mmHg, respectively) and did not increase renal blood flow (+12±10 vs. +52±10* mL/min). Effects on heart rate and cardiac output were similar. Urinary sodium excretion increased 128±18 µEq/min with BNP 3-32 and 338±40* µEq/min with BNP 1-32. Urine flow increased 1.1±0.2 mL/min with BNP 3-32 and 2.8±0.4* mL/min with BNP 1-32. Plasma BNP immunoreactivity was reduced with BNP 3-32 suggesting accelerated degradation. Conclusion: In this study, BNP 3-32 showed reduced natriuresis and diuresis and a lack of vasodilating actions compared to BNP 1-32.