The best sampling practice is necessary to the microbiological determination of the intravascular catheter associated infection. Authors examined the results of blood cultures in the Intensive Care Unit of University of Szeged between 2002 and 2004. During this period 2757 blood cultures of 211 patients were examined. 14.5%-15% of the blood cultures were positive and 70-91% of the positive blood cultures become positive within 48 hour. Most of the positive samples were taken from colonised central vena or arterial catheter and only some cases were proved catheter associated bloodstream infections (4-3-2 cases). In this ICU the colonised catheters were removed so the number of catheter-associated infections minimized and avoided the overuse of antibiotic.