The intravenous infusion has become indispensable in modern medical therapy, but infection, especially infusion associated septicemia, remains a life threatening hazard. In 1970 to 1971 a nationwide epidemic of nosocomial Gram negative septicemia, traced by the Center for Disease Control to one supplier's contaminated infusion products, dramatically focused attention on the problem of infusion related infection. Contamination of the intravenous system can occur at virtually any point, from the time of manufacture until the infusion is terminated in the hospital. Once contaminated, the intravenous cannula and its adherent thrombus can serve as an intravascular nidus for the proliferation and dissemination of microorganisms. Some pathogens grow luxuriantly in infusion fluids at room temperature, attaining concentrations exceeding 105 organisms per millilitre in 24 hours. Moreover, contamination of infusion fluid in use is probably common and must now be recognized as a potential cause of septicemia.