The devastating transfusion reaction that can occur after the infusion of blood contaminated with bacteria has prompted blood banks to adopt practices designed to minimize the possibility of bacterial contamination. There are four recognized sources of contamination of blood collected for transfusion: 1) prior contamination of the bag or the anticoagulant solution; 2) airborne contamination of the needle; 3) inadequate skin preparation including coring of the skin; and 4) bacteremia in the donor. The use of plastic collection bags and specially designed needles, and the recognition of the importance of aseptic technique have drastically reduced the incidence of serious transfusion reactions due to contamination. The history obtained from the donor prior to phlebotomy also eliminates many donors who could have bacteria in their blood at the time of donation. Improved collection techniques and the deferral of potential high risk donors have made serious reactions from contaminated blood a rare occurrance.