I n t r o d u c t i o n: Interactions between oral microbiota and systemic diseases have been suggested. We aimed to examine the composition of oral microbiota with reference to antioxidative defense and its correlation with clinical state in Crohn’s disease (CD) in comparison to ulcerative colitis (UC). Ma t e r i a l s a n d Me t h o d s: Smears were taken from the buccal and tongue mucosa of patients with CD, UC and controls, and cultured with classical microbiology methods. Bacterial colonies were identified using matrix-assisted laser desorption/ionization (MALDI) with a time-of-flight analyzer (TOF). Blood morphology and C-reactive protein (CRP) were analyzed in the hospital laboratory. Antioxidative defense potential (FRAP) was determined using spectrophotometry in saliva and serum. R e s u l t s: Oral microbiota in CD patients were characterized by lower diversity in terms of the isolated bacteria species compared to UC and this correlated with reduced FRAP in the oral cavity and intensified systemic infl ammation. Oral microbiota composition in CD did not depend on the applied treatment. In CD patients, a negative correlation was observed between the FRAP value in saliva and serum and the CRP value in serum. Individual differences in the composition of oral microbiota suggest that different bacteria species may be involved in the induction of oxidative stress associated with a weakening of antioxidative defense in the oral cavity, manifested by ongoing systemic inflammation. C o n c l u s i o n s: Analysis of both the state of the microbiota and antioxidative defense of the oral cavity, as well as their referencing to systemic inflammation may potentially prove helpful in routine diagnostic applications and in aiding a better understanding of CD and UC pathogenesis associated with oral microbiota.