Early appropriate treatment of bacteremia is important in minimizing morbidity and mortality. Standard blood culture methods are not optimal since several days are often required for recovery and identification of organisms which may be present in the blood. The use of a membrane filter technique allows one to grow any organisms present in blood much more rapidly than by broth or pour plate culture. Furthermore, growth is in the form of typical colonies on the surface of solid media, and a series of rapid diagnostic tests may be used to provide speedy identification. Use of membrane filters also facilitates removal by washing of normal antibacterial factors and antimicrobial drugs which may be present in blood. Although the filter technique yielded the most rapid growth, broth culture and whole blood pour plates yielded more positive cultures and use of all three systems was necessary for maximal recovery of organisms in blood cultures. Data on quantitative aspects of bacteremia in the antimicrobial era are also presented. The number of low level bacteremias (10 colonies/ml or less) is surprisingly high. This is particularly true for gram-negative bacilli; antimicrobial therapy at the time of culture undoubtedly influenced these results greatly. Finally, suggestions are given for a much simpler and more efficient membrance filter blood culture technique.