In this study, the measurement of blood pressure values, glomerular filtration rate (GFR, inulin clearance), renal plasma flow (RPF, PAH clearance), the filtration fraction (GFR/RPF), natiuresis and proximal sodium resorption (measured by lithium clearance), was performed at rest and during a computerised psychological stress test (Stroop word color conflict test) in 12 normotensive and 10 hypertensive subjects. The stress induced in the normotensives induced a significant increase of the filtration fraction and proximal tubule sodium resorption. The hypertensive kidney, submitted to a basal vasoconstriction greater than that of the normotensive kidney, does not react to stress. In the hypertensives, proximal sodium resorption occurs but is not significantly greater than at rest. In the long-term, the increased sodium resorption during stress could contribute to the development and the persistence of essential hypertension.