The study was performed to detect the in Nitro activity of tigecycline in multidrug-resistant Acinetobacier isolates from patients in Hacettepe University Adult Hospital, Turkey The microorganisms were isolated from clinical specimens of patients with respiratory and bloodstream infections. Thirty (66.7%) of the 45 inpatients were in ICUs. In vitro activity of imipenem, meropenem, ceftazidime, ciprofloxacin and aztreonam in 124 Acinetobacter species isolated was evaluated by microdilution test. Overall, 51 (41%) Acinetobacter spp. were found to be resistant to 0 antibiotics belonging to different antimicrobial classes and defined as multidrug-resistant (MDR). Among the MDR Acinetobacter spp. 32 (62.7%) were Acinetobacter baumannii and 19 (37.3%) Acinetobacter lwoffii. In vitro activity of tigecycline against MDR isolates were studied by E-test. Each MDR isolate was also tested for metallo-beta-lactamase (MBL) production using CLSI guidelines. Forty-five (88.2%) of the isolates were found to produce MBL. The MIC(90)s of all antimicrobial agents tested except tigecycline were >= 64 mu g/ml whereas the MIC50 and MIC90 of tigecycline were found 1 mu g/ml and 1.5 mu g/ml, respectively. ERIC-PCR results revealed that bloodstream and respiratory isolates had nine and six different patterns, respectively. In conclusion, tigecycline has been shown to have potent in Nitro activity against MDR Acinetobacter spp. and might be of therapeutic value in the treatment of. infections due to MDR Acinetobacter spp., including those harbouring MBLs. Further clinical trials are needed to confirm the efficacy of tigecycline in the management of MDR Acinetobacter infections.