Insufficient sleep contributes to an increased risk (e.g. ~60%) of hypertension. While BP is influenced by renal regulation of sodium and water, the underlying mechanism involved the modulation of renin-angiotensin-aldosterone-system (RAAS) by sleep deprivation is unknown. This project investigated the RAAS regulation of water and salt balance (e.g. urine output, sodium excretion) during prolonged sleep deprivation in humans. Twenty-six subjects completed a highly controlled 7-day in hospital study. They were randomly assigned to an 88-h total sleep deprivation (TSD; N=17) condition or an 8-h/night sleep control (SC; N=9) condition. Twenty-four-hour urinary output and sodium excretion value were measured from baseline (Day 2) to recovery (Day 7). Both TSD and SC groups showed continuous increases in sodium excretion during experimental period compared to baseline. The increases in TSD were significantly higher compared to SC. In addition, there was a dose dependent effect of TSD on sodium excretion. Urinary output significantly increased from baseline, to 24-h and 72-h during TSD, but remained at baseline levels throughout days in SC group. In conclusion, prolonged TSD significantly increases sodium excretion and urinary output from the body compared to control group, despite similar water and sodium intake levels between two groups. In addition, the increases of sodium excretion are also dose dependent during TSD.