Although neurogenic abnormalities have been postulated to be involved in the pathogenesis of borderline hypertension, no direct evidence has been documented. We continuously recorded muscle sympathetic nerve activity (MSNA) using a microelectrode in the tibial nerve, along with arterial pressure (AP) and heart rate (HR) during the cold pressor or isometric handgrip test in 16 male adolescents with borderline hypertension (BHT) and 10 normotensive adolescents (NT). Baroreflex changes in MSNA were also assessed during the pressor responses to intravenous phenylephrine. During the cold pressor test, both MSNA and AP gradually increased, but the HR responses were inconsistent. The resulting changes in MSNA, AP and HR were all augmented in BHT compared with NT. By contrast during the isometric handgrip test, MSNA, AP, and HR increased in both groups, but none of the differences between the groups was significant. Furthermore, baroreflex inhibition of MSNA were significantly reduced in BHT. Thus, some neurogenic abnormalities exist in BHT, which can be easily detected by recording MSNA.