Neonatal sympathectomy reduces arterial pressure in spontaneously hypertensive rats (SHR). In SHR transplanted with a kidney from sympathectomized SHR arterial pressure was lower and less sodium-sensitive than in SHR transplanted with a kidney from hydralazine-treated SHR. This study was performed to identify underlying renal mechanisms. Examination for differential renal mRNA expression of nine a priori selected genes revealed robust differences for renal medullary expression of the NADPH oxidase subunit p47phox. Therefore we investigated the effects of neonatal sympathectomy on renal mRNA expression of NADPH oxidase subunits, NADPH oxidase activity and renal function. In ten-week-old sympathectomized SHR on 0.6% NaCl diet medullary p47phox and gp91phox expression was 40% less than in hydralazine-treated SHR. Also after 1.8% NaCl diet, medullary p47phox mRNA expression was lower in sympathectomized than in hydralazine-treated SHR. Sympathectomized SHR had lower cortical (-30%, p < 0.01) and medullary (-30%, p < 0.05) NADPH oxidase activities than hydralazine-treated or untreated SHR. GFR, RBF, medullary blood flow and fractional Na+ excretion in kidney grafts from sympathectomized and hydralazine-treated donors (n = 8 per group) were similar at baseline and in response to a 20 mmHg rise in renal perfusion pressure. Renal vascular resistance (RVR) was lower in kidneys from sympathectomized than from hydralazine-treated donors (25±2 mmHg*min*ml^-1 vs. 32±4 mmHg*min*ml^-1, p < 0.05). The results indicate that the sympathetic nervous system contributes to the level of renal NADPH oxidase activity and to perinatal programming of alterations in renal vascular function that lead to elevated RVR in SHR.