The organisms isolated in hemoculture and their antimicrobial susceptibility change with years. Tehese changes have to be determined by medical centers in order to start appropriate empirical therapy. The purpose ot this study was to determine the micoroorganisms in hemocultures and their antimicrobial susceptibity in a major medical center in İzmir, Turkey. The blood samples sent to Clinical Microbiology Laboratory, Izmir Teaching and Research Hospital, İzmir, in 2003 were processed by the use of BACTEC 9050 Blood Culture System. The organisms detected in positive cultures were identifed by conventional identification methods and by gram-positive, gram-negative Crystal ID-Kit (BBL) when necessary. Antibiotic susceptibility of the strains was investigated by disc diffusion method in accordance with National Comittee for Clinical Laboratory Standarts (NCCLS). Microorganism were isolated in 157 of 1252 patients' blood cultures. Of all 54% gram positive cocci, 41% gram negative bacilli, 4% Brucella species, and 1% yeasts were isolated. Staphylococcus species were 85% of all gram positive cocci and Enterobacteriaceae were 80% of all gram negative bacilli. When the antimicrobial susceptibilty was investigated, the methicillin resistance among coagulase-negative staphylococci was 58% and among S. aureus was 18%. All the gram positive cocci were suspectible to glycopeptides. While there were no resistance to carbapenems in Enterobacteriacea species, the highest resistance rate (57%) was seen to ampicillin. Extended-spectrum beta lactamase (ESBL) was detected in 10% of E. coli and 27% of Klebsiella species. Even there were no resistance to ceftazidime, cefepime, aztreonam, quinolone, aminoglycosides in isolated P. aereginosa but resistance was detected in one strain to carbapenems and one other strain to piperacilline-tazobactam. When the other nonfermentatif microorganism were investigated, all were resistant to ampicillin, cefazolin, aztreonam, gentamicin, tobramycin, carbenisilin and the resistance rate to carbapenem, quinolone, amikacin and netilmicin were 80%, 60%, 80%, and 40% respectivery. In cases of high mortality and morbidity like sepsis, the importance of taking blood cultures in appropriate time and under appropriate conditions, using the automatic systems, identification of the isolated microorganisms and performing the antimicrobial suspectibility test were emphasized.