Our current understanding of the molecular mechanisms underlying host-parasite interaction in the establishment of persistent infections transmitted through blood transfusion permits us to develop strategies for their prevention. Because of rigorous screening to prevent transmission of blood-borne infections, the transfusion of blood and blood products has already achieved an unprecedented level of safety. The "window period" viraemia can be further reduced by screening donated blood with nucleic acid testing (NAT) technology now being introduced in Europe and the U.S.A. Both immunological and virological risks of transfusion can be reduced by photodecontamination and universal leukofiltration performed at the blood processing facilities. Unquestionably, progressive improvements in transfusion safety leads to an escalation in the cost of our blood supply; therefore, cost effectiveness, quality control, and regulatory issues have become topics of considerable importance.