Blood-culture procedures must be designed to overcome the intermittency and low order of magnitude of most bacteremias and fungemias and to inhibit any antimicrobial properties or components of the blood. Among the several variables affecting yields, the volume of blood cultured appears to be most important. It is recommended that at least 10 ml, and preferably 20-30 ml, of blood be obtained for each of two to three separate cultures. More than three separate blood cultures per septic episode is rarely necessary. Other issues involve the systems used for blood culture and the procedures used for their examination.