Infection, bacteremia, and sepsis are frequent complications in critically ill patients. Ideally, the infectious agent is readily identified to facilitate timely treatment to promote the patient's recovery. Use of blood cultures is one method of identifying the pathogen. Fever is the primary indicator for obtaining blood samples for culture, but other indicators may be considered, depending on the patient's medical history and condition. Use of appropriate techniques when collecting blood samples for culture will decrease contamination and improve the likelihood of identification of the infectious agent. One new technique being tested for the identification of pathogens that cause bacteremia involves genetic technology and the polymerase chain reaction. The polymerase chain reaction is used to identify the DNA of bacteria that are present in the blood. Blood cultures may not always result in identification of the pathogen because the organism may not grow once placed in culture medium. This new method that uses the polymerase chain reaction may be more sensitive than blood cultures because it requires only DNA from bacteria. Although early studies have not been conclusive in terms of the benefits of this new technology, additional research will improve methods for identification of pathogens in critically ill patients.