For the treatment of subclinical mastitis in lactating cows due to Gram-positive cocci susceptible to pirlimycin including staphylococcal organisms such as Staphylococcus aureus, both penicillinase-positive and penicillinase-negative, and coagulase-negative staphylococci; streptococcal organisms including Streptococcus agalactiae, Streptococcus dysgalactiae and Streptococcus uberis.