A Guadalupe fur seal (Artocephalus townsendi) was admitted to The Marine Mammal Center (TMMC) and while under extended rehabilitation it suddenly became weak. Blood was drawn for the medical work-up, and a profound anemia with a PCV of 6 was discovered. The fur seal had appeared normal, with a normal appetite in the weeks leading up to this discovery, however it weighed only 13 kg, and not been gaining weight. A clinically healthy California sea lion (Zalophus californianus) was designated as a blood donor, and was anesthetized using a preanesthetic dose of 0.02 mg/kg atropine i.m., followed ten minutes later by 1.7 mg/kg Telazol i.m. Blood was collected from the jugular vein into a bag containing acid-citrate-dextrose (ACD). The blood was taken directly to the fur seal which was lightly anesthetized with isoflurane gas. The blood was delivered through a commercially available blood administration set with a filter. Three hundred ml of whole blood was delivered by an intraosseous route through a 18 gauge spinal needle placed into the deep trochanteric fossa of the femur. At the end of the procedure, the PCV of the fur seal was 12, and the animal appeared weak, but comfortable. The animal was given 3 cc multiple vitamin B, 400 mg vitamin E i.m., 20mg vitamin K i.m., 46 mg enrofloxacin i.m., 100 mg prednisolone sodium succinate i.v. and 20mg iron i.m. The fur seal was given hematinics over the next ten weeks. It recovered uneventfully, and was released at a weight of 25 kg, and a PCV of 38.