In dry cow therapy (DCT), antibiotics are usually injected direct into the mammary gland after the last milking of the lactation. Most products are designed to eliminate existing intramammary infections (IMI) caused by Staphylococcus aureus and Streptococcus agalactiae and to prevent the establishment of new IMI caused by major pathogens during the early non-lactating period (Nickerson et al. 1999). Systemic therapy has been attempted as a way of improving the cure rates of intramammary treatments of clinical and subclinical mastitis during lactation (Ziv, 1980a; Calvinho et al. 1988; Owens et al. 1988). For systemic therapy to be useful, effective passage of the drug from blood to the foci of infection must be achieved. Maintaining an effective antibacterial concentration in the udder depends on the physicochemical properties of the drug, the dose, the bioavailability of the injected formulation, and the sensitivity of the pathogen (Ziv et al. 1980a, b). The theoretical pharmacokinetic and pharmacodynamic basis for systemic DCT has been reported (Soback, 1988). When used in an attempt to improve cure rates of IMI, subcutaneous injection of tilmicosin at drying-off was ineffective against Staph. aureus IMI (Nickerson et al. 1999) and intramuscular (i.m.) oxytetracycline, in combination with intramammary cephapirin dry-cow treatment did not improve the cure rate for Staph. aureus mastitis (Soback et al. 1990a; Erskine et al. 1994). Nevertheless, i.m. tylosin treatment 2 weeks before the expected day of calving decreased IMI after calving (Zecconi et al. 1999) and subcutaneous norfloxacin nicotinate applied at the cessation of milking proved useful in controlling Staph. aureus infections (Soback et al. 1990a). Moreover, the incidence of this pathogen after systemic DCT may be significantly lower compared with untreated control groups (Soback et al. 1990a, b).