B-type natriuretic peptide (BNP) is a cardiac hormone secreted predominantly from the ventricles in response to increased ventricular pressure. Along this line, hypertensive patients with left ventricular hypertrophy typically have high circulating BNP concentrations. BNP has natriuretic and vasodilatory actions. Obese persons have low circulating BNP concentrations, and a relative lack of this natriuretic and vasodilatory factor could contribute to obesity-related hypertension. The relationship between BNP, BP, left ventricular mass (LVM), and left ventricular filling pressure among obese persons is not clear. To address this issue, we studied 98 healthy obese medication-free men with normal left ventricular ejection fraction. We measured BP using 24 -h ambulatory (A) BP recordings, LVM and E/e', an estimate of left ventricular filling pressure, using echocardiography, and fasting BNP in serum. Mean systolic ABP ± SD was 114 ± 4 mm Hg in 1st and 149 ± 8 mm Hg in 4th systolic ABP quartile, P < 0.001. LVM and E/e' increased across systolic ABP quartiles (mean LVM±SD: 81.5±13.7 g/m2 in 1st and 100.1 ± 26.7 g/m2 in 4th quartile, P = 0.018; mean E/e'±SD: 5.3±1.6 in 1st and 7.0 ± 2.0 in 4th quartile, P = 0.002). In contrast, serum BNP did not increase across systolic ABP quartiles (median (IQR): 6.7 (3.1-12.3) pg/ml in 1st and 5.3 (2.8-9.7) pg/ml in 4th quartile, P = 0.75). Unexpectedly, among healthy obese medication-free men, serum BNP does not increase with higher systolic ABP despite evidence of BP-related increases in LVM and E/e'. This further suggests that a relatively low amount of circulating BNP could contribute to obesity-related hypertension in its early stages.