The efficacy of supplemental fresh frozen plasma (FFP) therapy after massive packed red cell (PRBC) replacement for hemorrhagic shock was studied in 22 conditioned dogs. Ten dogs were randomized to received FFP, balanced electrolyte solution (BES), and PRBC, while 12 dogs received BES and PRBC. Coagulation factor activity for Factors I, II, V, VII and VIII, as well as antithrombin III (AT III), prothrombin time, partial thromboplastin time, and thrombin time, were measured at preshock, postshock, postresuscitation, and postshock day two. All coagulation factor activities fell with shock and decreased further with resuscitation in both groups. Factor II (a procoagulant) and AT III (an anticoagulant) fell significantly less after resuscitation in the plasma dogs; otherwise, no postresuscitation differences were seen. The changes in factor activity from postresuscitation until day two reflected factor half life and molecular weight, independent of FFP therapy. These data show that prophylactic FFP therapy does not efficiently restore coagulation activity. Consequently, routine FFP therapy for its procoagulant effects after hemorrhagic shock should be abandoned pending controlled studies in man.