Hyperacute and renal allograft failure, whether due to rejection or other mechanisms, such as perfusion injury, is usually associated with extensive intraglomerular fibrin deposition and allograft loss. Defibrination with ancrod was used to treat a patient with hyperacute renal allograft failure and extensive glomerular fibrin deposition and necrosis. The patient's plasma had normal fibrinolytic activity but a complete absence of the ability to generate prostacyclin-like activity from rat aortic endothelium "in vitro". Treatment was associated with complete recovery of renal function, disappearance of glomerular fibrin, and restoration toward normal of glomerular structure.