Background: Elevated plasma endothelin-1 (ET-1) was found in end-stage renal failure (ESRF). However, there are discordant reports on the influence of hypertension on plasma ET-1 in ESRF and on the effect of hemodialysis on ET-1 concentrations. Aim: To compare the time course of plasma ET-1 during hemodialysis in hypertensive (HT) and normotensive (NT) ESRF patients. Methods: Plasma ET-1 and mean blood pressure (MP) were measured in 12 HT patients and 11 matched NT patients on maintenance hemodialysis at baseline (B), after a 2.5–3.5 h hemodialysis with ultrafiltration (P1) and after a subsequent 1 h isovolumic dialysis (P2). Results: In HT patients, plasma ET-1 increased at P1 with no further change after P2 (B vs. P1 and P2, p < 0.05). In NT patients, ET-1 levels were similar at B, P1 and P2. In HT, but not in NT subjects, volume loss correlated with change of ET-1 at P1. In HT patients, MP fell during P1 and tended to return towards baseline at P2. In NT patients, MP dropped after P1 and remained lower also at P2. Conclusion: Hypertensive ESRF subjects exhibit potentiated ET-1 release on hemodialysis, possibly stimulated by volume depletion with sympathetic activation, which may attenuate hypotensive hemodialysis effects thus contributing to hypertension in ESRF.