New Zealand white rabbits, were given 30 ml of goat serum i.v. This procedure resulted in an immediate decrease in platelet count, fibrinogen and levels of coagulation factors II, V, VII and X, due to consumption coagulopathy. These factors returned toward baseline levels approximately 12 h after the injection. Plasma from rabbits who had received goal serum 48 h previously (donor rabbits) was injected into recipient rabbits. This procedure resulted in a slight rise in the level of coagulation factor II (range, 20%-30%) and a significant rise in factors V (35%-75%), VII (35%-235%) and X (35%-75%) in the recipients. When plasma from control donor rabbits who had not received goat serum was injected into recipients, there was no change in these coagulation factors. The reduction in coagulation factor levels in donor rabbits apparently induces a coagulopoietin for each factor or one coagulopoietin for all factors which stimulates increased synthesis and/or release of these factors in recipient rabbits.