Abstract Thirst induced by subcutaneous injection of a hyperoncotic colloidal solution and associated with decreased intravascular fluid volume (hypovolemia) was contrasted with thirst induced by subcutaneous injection of hypertonic NaCl solution and associated with hyperosmolarity and decreased intracellular fluid volume. Intragastric preloads of isotonic NaCl solution reduced “hypovolemic thirst” more efficiently than did equal preloads of distilled water, whereas the opposite was the case with “hyperosmolar thirst.” However, when given a choice between 0.15 M NaCl and water to drink, rats did not show differential preference behavior as a function of colloid or 1.0 M NaCl treatment but tended to prefer the saline solution to water under both conditions. While the preloading data support the notion that thirst is mediated by two types of receptors, one responsive to the volume and the other to the effective osmolarity of the intravascular fluid, the preference data indicate that fluid intake is not determined solely by homeostatic factors but may also be influenced by other factors such as the palatability of the fluid.