At its very early phase, septic shock is characterized by severe hypovolemia related to abundant fluid losses, increased venous compliance and maldistribution of extracellular fluid (interstitial edema, splanchnic pooling). It results in a drop in venous return and cardiac output. Volume expansion, with crystalloids or colloids produces a hyperdynamic state with high cardiac output and low peripheral resistances. The quantity of liquid administered rather than its composition is the main determinant. Clinical examination and hemodynamic monitoring (Swan-Ganz catheter) appear to provide the most useful criteria to assess the limits of liquid administration. Better understanding in the mechanisms of circulatory dysfunction due to the inflammation cascades might soon lead to a new approach in fluid therapy.