To identify lower respiratory tract pathogens and their in-vitro antibiotic susceptibilities in Turkish cystic fibrosis (CF) patients, a total of 383 sputum cultures were evaluated from 45 OF children in 168 symptomatic and 215 control periods over 25 months. Microorganisms were isolated in 252 of the cultures. The isolation rats was 82 percent for symptomatic periods and 53 percent for control periods. The most common microorganism was P. aeruginosa in the symptomatic period and S. aureus in the control period. Other microbiological species included E. coli, H. influenzae, K. pneumoniae, S. epidermidis, beta-hemolytic streptococcus, H. parainfluenzae, K. oxytoca, E. aerogenes and E. aglomerans. P. cepacia was not found, In 20 cultures more than one microorganism was isolated at the same time. In in-vitro conditions, high susceptibility rates were detected to amikacin, ciprofloxacin and cettazidim for P. aeruginosa; cefuroxime, ceftriaxone, amikacin, cephalothin, chloramphenicol and erythromycin for S. aureus; amikacin and ceftriaxone for E. coli; ampicillin-sulbactam, amoxicillin-clavulanate, cefuroxime, ceftazidime, ceftriaxone and aztreonam for H. influeanzae; and aztreonam and amikacin for K. pneumoniae, Lower respiratory tract pathogens and their antibiotic susceptibilities in Turkish CF children were not significantly different from those indicated previously in the literature.