Isovolemic exchange perfusion of conscious normal and splenectomized rats to a Hct of +/- 3% with the perfluorocarbon based oxygen transport fluid, Fluosol-DA 20%, is characterized by: 1) a greater than projected depression of fibrinogen and the plasma globulins and 2) a rapid regeneration of these and certain other plasma proteins. Similar responses were observed in a study of PFC resuscitation of hemorrhagic shock in splenectomized dogs in which there was a selective depression of the platelets, the plasma globulins, IgG and fibrinogen. In the rats, the red cells and platelets required 14-21 days to return to control levels while the leukocytes returned to normal in 1-2 days. The globulins and fibrinogen exhibited a transient rebound response at 3 and 12 hours post exchange respectively with total protein levels restored to control levels at 48 hours. In the shock study, the leukocytes, which remained at control levels throughout the shock period and for 1 hour post resuscitation were 2.5x control levels at 24 hours. The platelets which were depressed to 20% of control levels following resuscitation remained depressed through the 24 hour time course of the study. Implicit in these results is the possibility that; A) thrombosis and B) immunosuppression may be caused by some component(s) of the perfusion/resuscitation fluid.