There are no published data that demonstrate that a greater magnitude of bacteremia, compared with a lower magnitude, is more likely to cause IE in humans. The magnitude of bacteremia resulting from a dental procedure is relatively low ( 104 colony-forming units of bacteria per milliliter), similar to that resulting from routine daily activities, and is less than that used to cause experimental IE in animals (106 colony-forming units of bacteria per milliliter).20,43,44 Although the infective dose required to cause IE in humans is unknown, the number of microorganisms present in blood after a dental procedure or associated with daily activities is low. Cases of IE caused by oral bacteria probably result from the exposures to low inocula of bacteria in the bloodstream that result from routine daily activities and not from a dental procedure. Additionally, the vast majority of patients with IE have not had a dental procedure within 2 weeks before the onset of symptoms of The role of duration of bacteremia on the risk of acquisi- tion of IE is uncertain.45,46 Early studies reported that sequen- tial blood cultures were positive for up to 10 minutes after tooth extraction and that the number of positive blood cultures dropped sharply after 10 to 30 minutes.24,45 51 More recent studies support these data but report a small percentage of positive blood cultures from 30 to 60 minutes after tooth extraction.43,52,53 Intuitively, it seems logical to assume that the longer the duration of bacteremia, the greater the risk of IE, but no published studies support this assumption. Given the preponderance of published data, there may not be a clinically significant difference in the frequency, nature, magnitude, and duration of bacteremia associated with a dental procedure compared with that resulting from routine daily activities. 