The goal of an antibiotic therapy consists in increasing the efficacy of the immunological defense mechanisms as self cure by reducing the number of pathogens. Therefore, pharmacological criteria as well as physiological and immunological factors have to be regarded with respect to a successful medication. A sufficient immunological defense is depending on a stable homoeostasis to ensure low new infection rates and acceptable cure rates. Especially during the early lactation stage problems may arise to maintain the cow in a physiological balance. Under such conditions the mastitis therapy should include the application of special drugs to support the immune system in addition to the application of antibiotics.