Mastitis is the most common and expensive disease. In general, about 20-40 % dairy cows from a herd are infected. The losses due to this disease range from less than 1000 to more than 1500 CZK per a cow and a year. The greatest loss associated with mastitis (ca. 60 to 80 %) arises from a reduced milk yield and quality. Other losses incurred are the premature culling, veterinary costs and increased labour input, in some cases also lower reproduction efficiency. Among the most effective measures of mastitis control belong the prevention and early treatment. These tasks can be performed on the basis of somatic cell content in milk.