There is usually no value in obtaining >5 blood cultures over 2 days unless the patient has received antibiotic therapy within the past 2 weeks. In patients who are not acutely ill and whose blood cultures remain negative, withholding antibiotic drugs for 48 hours or longer while additional blood cultures are obtained may be considered, to determine the cause of IE. In patients with acute IE who are severely ill and unsta- ble, 3 separate venipunctures for blood cultures should be performed over a short period such as 1 to 2 hours (Table 3) and empirical antibiotic therapy initiated. Continuous- monitoring blood culture systems such as BACTEC (Becton, Dickinson and Co, Franklin Lakes, NJ) and newer molecular identification methods are more rapid and more sensitive than more conventional methods. If fastidious or unusual organisms are suspected, the director of the micro- biology laboratory should be consulted for help in diagno- sis. Culture of arterial blood is not useful because it does not increase yield. Recommendations 1. Blood cultures should be drawn for patients with fever of unexplained origin and a pathological heart murmur, a history of heart disease, or previous endocarditis (Class I; Level of Evidence B). 2. It is reasonable to obtain 3 blood cultures by sepa- rate venipunctures on the first day, and if there is no growth by the second day of incubation, to obtain 2 or 3 more (Table 3) (Class IIa; Level of Evidence B). 3. In patients who are not acutely ill and whose blood cultures remain negative, withholding antibiotic drugs for 48 hours while additional blood cultures are obtained may be considered to determine the cause of IE (Class IIb; Level of Evidence C). 4. 