Hematogenous dissemination of organisms occurs in many spirochetal diseases, including Lyme disease and syphilis. Although syphilis has been transmitted by transfusion, in the vast majority of cases, only fresh blood products were involved, in part because Treponema pallidum survives poorly when refrigerated in citrated blood. Because of the rising incidence of Lyme disease in certain areas, whether its causative agent, Borrelia burgdorferi, could survive under blood banking conditions was studied. Dilutions of stock cultures of two strains of B. burgdorferi were inoculated into samples of citrated red cells (RBCs). Viable spirochetes were recovered from RBCs inoculated with 10(6) organisms per mL, after refrigeration for as long as 6 weeks. It is concluded that B. burgdorferi may survive storage under blood banking conditions and that transfusion-related Lyme disease is theoretically possible.