We studied the time course and interactions of hemodynamic, oxygen transport, colloid osmotic pressure (COP), and blood volume responses to 500 ml of crystalline hemoglobin (Hgb), 500 ml of whole blood (WB), 1,000 ml of Ringer's lactate (RL), and 500 ml of plasma protein fraction (PPF) given in random order to 12 mongrel dogs subjected to hemorrhagic shock by the standard Wiggers' technique. In general, hemodynamic and oxygen transport responses were greater and more prolonged after the colloids than after RL. These responses were related to concomitant improvement in blood volume and COP. Of the colloids, Hgb appeared to produce somewhat greater hemodynamic and oxygen transport changes. This was particularly evidenced by comparison of these responses when each fluid was the first agent used after the hemorrhage. By virtue of its capacity to increase COP and plasma volume and to carry oxygen, Hgb improved both the gross circulation and the tissue perfusion, as indicated by cardiovascular hemodynamics and bulk oxygen transport variables.