The authors induced acute blood loss in dogs and examined the changes in hemodynamics, hemodilution, blood coagulation acid-base balance and tissue respiration. They found that the most favourable hours for initial renimation were the first two hours. They used the Bulgarian plasma substitute reoisodex with very good effect on the indicated parameters and microcirculation. As a result of this the time for the appearence of irreversible stage in grave hypovolemia was prolonged with hours.