Experiments were conducted on nembutal-anesthetized cats; a study was made of the dynamic viscosity of the blood, and also of an aggregation capacity of the blood formed elements for two hours of the postresuscitative period. There was established an increase in the viscosity both in the zone of a low (1.82 dynes/cm2) and high (10.94 dynes/cm2) sear stress. A definite role in increase of the blood viscosity is played by a rise in the hematocrite index and by enhanced aggregation capacity of the blood formed elements.