Patients with cystic fibrosis (CF) develop as a result of this disease chronic bacterial lung infections (mixed infections), which often lead to premature death. It has been investigated whether the periodontal sulcus of children with CF is a potential reservoir for the bacteria tested, thus providing a possible source of pulmonary infections and whether the increased antibiotic treatment of pulmonary infections leads to increased resistance of the bacteria. The microbial colonization of the sulki of healthy and CF- children was compared, as well as the microbial colonization of the sulki and sputum of CF-children. Using standardized methods, the samples were processed anaerobically and aerobically and the bacteria identified as facultative or obligate anaerobic bacteria. Subsequently, the same pairs of obligate anaerobic bacteria from the sputum and the sulki of the CF children were examined for their sensitivity to various antibiotics. The microbial colonization of the tooth pockets differed only insignificantly from each other in both groups. Likewise, the same antibiotic-tested couples showed little difference in their resistance patterns. Because of this, it is obvious to suspect a link between sputum-derived lung infections and the periodontal sulcus.