Staphylococci are an increasing cause of bloodstream infections. Rapid reliable identification of these organisms is essential for accurate diagnosis and prompt effective treatment. We evaluated the ability of the VITEK 2 system (bioMĂ©rieux, Inc, Hazelwood, Mo.) to identify these organisms rapidly and accurately. A total of 405 clinically relevant nonduplicate staphylococcal isolates (Staphylococcus aureus, n â«Ű⏠130; coagulasenegative staphylococci, n â«Ű⏠275) collected from blood cultures were tested. VITEK 2 results were considered correct when they were identical to those furnished by the comparison method based on the ID 32 STAPH system (bioMĂ©rieux, Marcy l'Etoile, France) plus supplementary manual testing. When discrepancies occurred, isolate identity was verified by molecular typing. The VITEK 2 correctly identified 387 (95.6%) isolates at the species level: 379 (including all but one [99.2%] of 130 S. aureus isolates and 249 of 275 [90.5%] coagulase-negative isolates) were identified by the automated reading; for the other eight, supplemental tests suggested by the manufacturer had to be used. Only one strain (0.2%) was misidentified (Staphylococcus hominis as Staphylococcus epidermidis), and four (1%), all S. epidermidis, were not identified. For the remaining 13 strains (including 10 S. hominis), the VITEK 2 system was unable to discriminate among two species, and no supplemental tests were suggested for conclusive identification. Over 90% of results were obtained within 4 h. These results suggest that the VITEK 2 system can provide rapid, accurate, and reliable species-level identification of staphylococci responsible for bloodstream infections, although there is room for improvement in the identification of certain coagulase-negative species, especially S. hominis.Bloodstream infections are a major cause of morbidity and mortality. The frequency, etiology, and epidemiology of these infections have changed over the years. Staphylococcus aureus is now recognized as an important cause of both hospital and community-acquired bloodstream infections (1,3,8,9,27,30). During the last 2 decades, the increased use of invasive procedures and broad-spectrum antibiotics, together with the growing number of immunocompromised and/or seriously ill patients, has led to the emergence of coagulase-negative staphylococci, particularly Staphylococcus epidermidis, and these organisms plays a prominent role in nosocomial bloodstream infections (1,2,3,8,9,17,18,29). Rapid and reliable species identification of these organisms is essential for accurate diagnosis and prompt effective treatment of these infections (6,7,10,16). Several manual and commercial identification methods have been developed and are now routinely used (4,5,15,23,24,25,26,31). The fully automated VITEK 2 system (bioMĂ©rieux, Inc, Hazelwood, Mo.) can provide identification results for gram-positive cocci in a few hours thanks to the improved sensitivity of its fluorescence-based technology, and this feature represents a major improvement over earlier versi...