Aim: The aim of this study was to evaluate in vitro the antibacterial effect of ozone on suspension of three different bacteria inoculated in prepared canals of extracted human teeth. Material and methods: Ozone was produced by special KP syringe of high frequency ozone generator Ozonytron (Biozonix, Munchen, Germany) from aspirated atmospheric air by dielectric barrier discharge and applied through the tip of the syringe to the prepared root canal. The microorganisms used were Enterococcus faecalis, Staphylococcus aureus and Staphylococcus epidermidis. Results: However, none of the methods was 100% effective against the three bacterial types in suspension. Application of ozone significantly decreased the absolute count of microorganisms (89.3%), as well as the count of each type of bacteria separately (Staphylococcus aureus 94.0 %; Staphylococcus epidermidis 88.6% and Enterococcus faecalis 79.7%). Ozone generated by KP syringe was statistically more effective compared to NaOCl as positive control, for Staphylococcus aureus and Staphylococcus epidermidis. Conclusion: The absolute count of Enterococcus faecalis was statistically decreased without a statistically significant difference between the tested group and positive control, respectively. Among the three types of bacteria in suspension, KP probe had the lowest antimicrobial effect against Enterococcus faecalis. Key words Dental Pulp Cavity; Root Canal Therapy; Anti-Bacterial Agents; Ozone; Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis Svrha: Svrha ovog istrazivanja bila je procijeniti in vitro ucinkovitost ozona na suspenziju triju razlicitih vrsta bakterija inokluiranih u obradene korijenske kanale ekstrahiranih ljudskih zubi. Materijal i metode: Ozon je proizveden od aspiriranog zraka uporabom specijalne KP brizgalice visokofre-kvencijskoga generatora ozona Ozonytron (Biozonix, MUnchen, Njemacka) S pomocu dielektricnog barijernog izboja, te nastavka na strcaljki postavljenog u pripremljeni korijenski kanal. Ispitivani su mikroorganizmi Enterococcus faecalis, Staphylococcus aureus i Staphyloccocus epidermidis. Rezultati: Ni jedna metoda nije pokazala 100-postotnu ucinkovitost u eliminaciji navedenih bakterija u suspenziji. Primjena ozona znacajno je smanjila ukupan broj mikroorganizama (89,3 %), te broj svake vrste bakterija posebno (Staphyloccocus aureus--94,0 %; Staphyloccocus epidermidis--88,6% i Enterococcus faecalis--79,7 %). Ozon proizveden KP brizgalicom bio je statisticki znatno ucinkovitiji u eliminaciji Staphyloccocus aureus i Staphyloccocus epidermidis u usporedbi S NaOCl-om kao pozitivnom kontrolom. Zakljucak: Ukupan broj Enterococcus faecalis bio je statisticki manji, no bez znacajne statisticke razlike izmedu ispitivane i pozitivne kontrolne skupine. Izmedu triju vrsta bakterija u suspenziji, primjena KP strcaljke pokazala je najmanju ucinkovitost u eliminaciji Enterococcus faecalis. Kljucne rijeci zubna pulpa, komora; korijenski kanal, lijecenje; antibakterijska sredstva; ozon; Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis