Recent major complications, hemoglobinuria with or without acute renal insufficiency, have occurred only with the transfusion during surgery of deglycerolized red blood cells resuspended in an artificial 5% albumin resuspension medium. No major complications have occurred with deglycerolized red blood cells resuspended in autologous plasma. Hemoglobinuria can be tolerated by normotensive, normovolemic individuals with normal renal function. However, hemoglobinuria associated with hypotension, increased antidiuretic hormone, dehydration, acidosis, and hemorrhage can precipitate acute renal insufficiency. Hemoglobinuria may occur secondary to infusion of supernatant hemoglobin or the intravascular liberation of hemoglobin from nonviable preserved erythrocytes.