The authors present the case of a young man with aplastic anemia who went into shock and died after several red blood cell unit transfusions. Immunohematological studies did not show any abnormality and blood cultures from patients and blood bags were negative. The ultrastructural findings, allied with current scientific knowledge, permitted the diagnosis of Bartonella sp. infection. In face of this diagnosis, two possibilities should be considered: the first one is that the patient was already infected by the bacteria before the last RBC unit transfusion. The pathogen could be involved in aplastic anemia etiology and in the failure to recover hemoglobin levels, in spite of the transfusions. The second possibility is that the RBC unit was contaminated with a Bartonella sp., which would have led to a state of shock, causing the death of the patient.33151-4