Drugs targeting VEGF (vascular endothelial growth factor) are often associated with rapid development of hypertension by a yet not fully understood mechanism. VEGF is expressed in renal epithelial cells and stimulates NO production. In the renal medulla, inhibition of NO formation by local L-NAME or by impaired endothelin-1 leads to hypertension. The present study was designed to test the hypothesis that VEGF receptor inhibitor treatment leads to hypertension through decreased renal medullary formation of NO and endothelin-1. With a single-center prospective observational design, patients with metastatic renal cell carcinoma (n=27) treated with the receptor tyrosine kinase inhibitor pazopanib were included in the study. Home blood pressure was measured, and plasma and urine samples were collected at baseline and after 4 and 8 weeks of treatment. After 4 weeks, systolic and diastolic blood pressures increased, whereas heart rate decreased significantly; urine protein/creatinine ratio increased significantly, whereas estimated glomerular filtration rate was unchanged. Urine nitrite/nitrate (NOx) and cGMP/creatinine ratios decreased significantly, whereas urine endothelin-1/creatinine ratio and FENa+ were unchanged. In plasma, NOx, cGMP, and brain natriuretic peptide decreased significantly, whereas endothelin-1 was significantly elevated. Blood leukocyte count decreased significantly with unchanged CRP (C-reactive protein). In summary, pazopanib treatment of patients with advanced renal cell carcinoma is associated with hypertension, proteinuria, myelosuppression, and decreased urine and plasma NO metabolites. Results are compatible with a significant role of reduced renal medullary NO bioavailability in VEGF inhibitor-induced hypertension.