European Erythema migrans Borreliosis and North American Lyme disease are closely related to syphilis. This implicates a potential risk of infection for blood recipients. Eighty-six of 3,157 blood donors tested showed IgG-antibodies against Borrelia Burgdorferi. From among 47 persons of this group who could be examined, clinical signs of diseased skin, joints or nervous system, not diagnosed before, were found or could be suspected in 13 cases. Since intrauterine transmission of Borrelia infection has been described, the inevitable question of whether this disease can also be transmitted as a result of blood transfusion becomes a major concern. As the pathogen can persist even in the presence of serum antibodies, it seems advisable to examine blood donors serologically, whenever Erythema migrans Borreliosis is suspected. Though further research is required to document a transfusion-transmitted Borrelia infection, infected persons should be treated to avoid serious or late manifestations.