The safety of treatment of renal hemorrhage from trauma with angiographic injection of autologous clot was investigated in rats by demonstrating the effect of various sizes of clot emboli on renal survival. A large amount of clot injected into the entire distal part of the renal arterial tree (equivalent to 20 cu cm in the human) was required to produce a 15% infarction. This large safety range is possibly due to the endogenous fibrinolytic capability of normal vascular endothelium.