Background: Mastitis is an economically important disease leading cost associated problems. The most accurate relationship between intramammary infection and somatic cell count (SCC) can be evaluated at quarter level when SCC exceeds 100.000 cells/mL. In subclinical mastitis, pathogens do not cause enough disruption in the alveolar tissue to be seen in the milk but SCC increase indicates the infected milk. Ozone (O-3) is an unstable polymerized oxygen created by the passage of air or oxygen over high energy electrodes within an ozone generator system or by ultraviolet light. The aim of this study was to compare the treatment efficacy of ozone (O-3) insufflation daily via latex free syringe in different doses (30-60-70 mu g/mL) and high dose O-3 insufflation (70 mu g/mL) with combination of antibiotic and only antibiotic treatment in dairy cows with clinical mastitis.