Central venous catheters from intensive care unit patients were subjected to microbiological methods (semiquantitative culture) and scanning electron microscopy in order to assess microbial attachment and correlate it with blood cultures. During the period of the survey, 59 patients with inserted central venous catheters were studied. The type of catheter used was nontunneled, noncuffed, single lumen, made of polyurethane. Blood samples for cultures were collected at the moment of catheter removal. Data on the patient's age, gender, catheter insertion site, and duration of catheterization were also obtained. From 63 catheters tips analysed, 30 (47.6%) showed microbial colonization. Infection proved to be more prevalent in 26 (41.3%) patients with catheters inserted via subclavia vein than in 2 (3.2%) inserted via the jugular vein. Infection was observed more frequently in catheters which were kept in place more than seven days. A. baumannii, Citrobacter freundii, E. aerogenes, P. aeruginosa and S. saprohyticus were isolated as causal agents of catheter-related bloodstream infections. The antimicrobial agent with greater in vitro activity against Gram-negative bacteria was imipenen and against Gram-positive were vancomycin, cefepime, penicillin, rifampin and tetracycline. The SEM analyses revealed biofilms on surfaces of all the catheters examined.