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Infusion of hypertonic saline produces an increase in thirst appreciation as well as increase in plasma Arginine Vasopressin (AVP) concentration, which may be estimated using thirst perception and/or plasma osmolality In this study, we examined the changes in thirst perception (TP), plasma osmolality (Posm) and plasma arginine vasopressin concentration (PAVP) as well as their relationships in dehydrated and oral saline loaded subjects. Forty (40) healthy subjects between the ages of 18 and 30 years were divided into 4 groups of 10 subjects (5 females and 5 males) each. Subjects in group A (dehydrated) were subjected to 18 hr fluid restriction, while those in B, C, and D orally ingested 7.1 ml/kg of 0.9%, 1.8% and 2.7% NaCl solutions respectively. TP was rated using the Visual Analogue Scale, VAS. Estimation of Posm was done using the standard formula and was also calculated from TP. PAVP was calculated from TP and Posm. The changes in TP in water restriction and salt loadings were similar in both males and females. However, the 2.7% NaCl sodium chloride solution intake induced a greater increase in TP than the 18 h fluid restriction. In females there was no significant difference between the measured and calculated Posm at 0 min, in groups A and D, whereas, values for group B (278.8±4.2 vs 292.0±2.9 mOsm/kgH2O) and C (282.6±4.1 vs 295.6±2.5 mOsm/kgH2O) differ significantly (p< 0.05). At 90 min, the calculated Posm was significantly higher than the measured Posm in group D (283.6±2.1 vs 312.0±0.8 mOsm/kgH2O, p< 0.05) only. In male subjects, there was no significant difference between the measured and calculated …