The proto-oncogene c-myb (and corresponding nuclear transcription factor, c-Myb) regulates the proliferation and differentiation of hematologic and vascular smooth muscle cells; however, the role of c-Myb in blood pressure regulation is unknown. Here, we show that mice homozygous for a hypomorphic c-myb allele (c-myb^h/h) conferring reduced c-Myb activity manifest reduced peripheral blood and kidney B220⁺ B-cells and have decreased systolic (104±2 versus 120±1 mm Hg; P<0.0001) and diastolic blood pressure (71±2 versus 83±1 mm Hg; P<0.0001) compared with WT (wild type) mice. Additionally, c-myb^h/h mice had lower susceptibility to deoxycorticosterone acetate-salt experimental hypertension. Although cardiac (echocardiography) and resistance artery (perfusion myography) functions were normal, metabolic cage studies revealed that c-myb^h/h mice had increased 24-hour urine output and sodium excretion versus WT. Reconstitution of WT mice with c-myb^h/h bone marrow transplant and chimeric bone marrow transplant using mice lacking B-cells (J_HT; h/h>WT and h/h:J_HT>WT, respectively) decreased blood pressure and increased 24-hour urine output compared with controls (WT>WT; WT:J_HT>WT). J_HT mice also had decreased systolic (103±2 versus 115±1 mm Hg; P<0.0001) and diastolic blood pressure (71±2 versus 79±1; P<0.01) and increased 24-hour urine output versus WT. Real-time quantitative reverse transcription polymerase chain reaction of kidney medulla revealed reduced V₂R (vasopressin receptor 2) expression in c-myb^h/h and J_HT mice. These data implicate B-cells in the regulation of V₂R and its associated effects on salt and water handling and blood pressure homeostasis.