Abstract
Transfusion of 500 ml of blood, contributed by a donor three days before the onset of Rocky Mountain spotted fever and refrigerated for 9 days, caused this disease in the recipient. The blood donor died of Rocky Mountain spotted fever after 6 days; rickettsias were identified in various tissues by immunofluorescence techniques. The recipient of the blood became mildly ill and recovered fully; specific antibiotic treatment was initiated on the 4th day of illness. Diagnosis of Rocky Mountain spotted fever was confirmed in the recipient by positive serologic reactions and isolation of Rickettsia rickettsii from blood after inoculation in animals [guinea pigs] and tissue culture.