To detect microorganisms in the blood it is necessary not only that the microbiologist uses reliable methods, but also that the clinician takes a sufficient number of blood samples at the right point in time using a correct method for drawing the blood. The best results are obtained if the blood sample is transferred to the culture media at the bedside. The media should contain anticoagulants, osmosis stabilizers and preparations to neutralize the microbial action of the blood (caused by intrinsic and extrinsic factors). Up until now sodium polyanetholsulfonate ("Liquoid") has proved to be the most suitable additive. The procedure used for blood culturing must enable growth of aerobes, anaerobes and microbes with cell-wall damage. Today, modern methods such as radiometry, impedance measurement and microcalorimetry are used or are in the process of being developed which facilitate screening for positive cultures. Antigens, cell-wall constituents and metabolites of bacteria and fungi present in the blood stream can be detected by means of counter-immunoelectrophoresis, the Limulus test and gas chromatography, without culturing being necessary. Concentration techniques such as filtration and centrifugation are also being refined to enable a more reliable and earlier detection of septicemia.