The aim of this study was to investigate the effects of the use of Theranekron alone or in combination with intramammary antibiotic therapy for the treatment of subclinical and clinical mastitis on the recovery rate from mastitis. The study material was composed of 177 mammary lobes of 63 Holstein cows with subclinical (groups S1 and S2) and clinical mastitis (groups C1, C2, C3, and C4). In all of the treatment groups, excluding group S2, the California mastitis test scores were determined to have decreased after treatment (P < 0.05). In groups C1, C2, C3, and C4, which were treated for clinical mastitis, the somatic cell count (SCC) values were observed to have decreased. The decrease in SCC values was statistically significant except in group C2 (P < 0.01). While the SCC values were observed to have decreased in group S1 (P > 0.05), which was treated with Theranekron alone, the same values were found to have increased in group S2, which was maintained for control purposes (P < 0.05). This study demonstrated that Theranekron D6 could be used as an alternative therapeutic for the treatment of clinical and subclinical mastitis, as it is authorized for the use in cattle with a withdrawal period of zero hours for meat and milk.