In an era of increasing managed care, during which costs are being scrutinized and management algorithms are being initiated at many levels of care, the use of strategies to prevent the development of active disease seems attractive. Treatment with antibiotics to prevent infection is one area where the potential benefits of disease prevention appear to far outweigh the costs. In fact, because they are relatively inexpensive and they can be administered easily, antibiotics are frequently administered prophylactically before procedures that might lead to bacteremia. The prophylactic use of antibiotics when an invasive procedure is performed in patients who have a prosthetic joint has been the subject of intense debate10,21,25,54,66,84,85,103,107,144,156,162. It has been estimated that as many as 500,000 total joint replacements are performed each year in the United States49, and this number is expected to grow as the population ages. Most of these replacements involve the lower extremities, with an estimated 125,000 total hip replacements, 84,000 hip hemiarthroplasties, and 179,000 total knee replacements being performed each year49. Approximately 5000 total shoulder replacements also are performed each year49. The effect of the implant on the patient's resistance to infection is important. Total joint implants have been shown to be surrounded by an immuno-incompetent, fibro-inflammatory zone that may impair the body's ability to eliminate bacteria around the implant51. This zone may become more stable with time, but a foreign object always represents a possible site for infection. The sites of prosthetic joints are placed at potential risk for infection by procedures that cause transient bacteremia. Because the average per capita incidence of dental visits in the United States is 2.1 …