Background: It is well known that compared to normotensive subjects (NormCon), patients with essential hypertension (EssHyp) have an exaggerated natriuretic response to acute saline loading, possibly associated with salt sensitivity of their blood pressure regulation. However, the exact mechanism is obscure. We hypothesized that the exaggeration of natriuresis in EssHyp is mediated by increases in mean arterial blood pressure (MABP), cardiac output (CO) and glomerular filtration rate (GFR) resulting in increased filtered sodium load and natriuresis. Methods: 10 EssHyp and 10 NormCon subjects were placed on low sodium diet (40 mmol/day) for 4 days and studied for two consecutive days. Day 1 was a time control; day 2 included a slow intravenous salt load (saline, 20 mmol/kg/min for 4 h). MABP was recorded every 10 min, CO was determined by impedance cardiography, and GFR measured by infusion of Cr51-EDTA. Results: On both study days, EssHyp showed small, identical increases in MABP, 106 mmHg to 113 mmHg. In NormCon, MABP was unchanged. Saline loading generated natriuresis in both groups, but in EssHyp peak natriuresis was higher (138±17 mmol/min) than in NormCon (82±20 mmol/min, p<0.05). GFR remained stable during the experiments, but EssHyp had slightly lower baseline values than NormCon (104 vs. 117 ml/min, p<0.05). Changes in diuresis were similar. EssHyp showed higher systemic vascular resistance (SVR) than NormCon at baseline (p<0.05), but increases in SVR during saline loading were similar. Conclusion: Patients with essential hypertension have an exaggerated natriuretic response to saline loading that is unrelated to MABP, GFR, and filtered load of sodium.