During severe hemorrhage the O-2-transport capacity of blood is reduced due to the loss of hemoglobin. This reduction is, however, fully compensated down to 25% hematocrit by augmentation of the minute volume consequent on the decrease of blood viscosity due to hemodilution, though this holds only on condition that myocardial contractibility and total blood volume are not impaired. The compensation of lost intravasal fluid is therefore prevailing importance, but the substitute need not be blood and may consist of a suitable colloid solution. Physiogel, a modified fluid gelatin, has proved to be excellent for this primary substitution of blood losses. The plasma derivatives should be reserved for special indications, particularly for treatment of oncotic deficit, and here highly concentrated (10-20% albumin) preparations are needed. Blood transfusions are indicated when the hemoglobin content falls below the critical limit of 25% hematocrit.