A total of 3,981 isolates from patients treated at intensive care units were collected in 25 European university hospitals during 1997 and 1998 as part of the SENTRY Antimicrobial Surveillance Program. Overall, the most important species isolated were Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, coagulase-negative staphylococci (CNS), Enterobacter spp., Haemophilus influenzae, Streptococcus pneumoniae, and Enterococcus faecalis. Thirty-nine percent of all Staphylococcus aureus isolates were resistant to oxacillin. All Staphylococcus aureus isolates were fully susceptible to linezolid and vancomycin. Moreover, all CNS isolates were susceptible to vancomycin and minocycline. All Enterococcus faecalis isolates were susceptible to vancomycin, and 99% of these isolates were also susceptible to ampicillin. The antimicrobial agents most effective against Pseudomonas aeruginosa isolates were amikacin, piperacillin/tazobactam, meropenem, and cefepime, with 87, 85, 84, and 83% of isolates being susceptible, respectively. Escherichia coli isolates were fully susceptible to carbapenems, and at least 99% of these isolates were susceptible to ceftriaxone, cefepime, and amikacin. The Enterobacter spp. were also highly susceptible to carbapenems, amikacin, and cefepime, with 99, 97, and 96% of isolates being susceptible, respectively. Haemophilus influenzae was susceptible to most of the antibiotics tested. Only 68% of the pneumococcal isolates were fully susceptible to penicillin, yet 100% were susceptible to a number of fluoroquinolones and vancomycin. There are still sufficient treatment options for patients infected with the most important bacterial species involved in infections in intensive care units. However, the situation for patients with Pseudomonas aeruginosa infections is critical.