Dairy farming is one of the most important economic activities in the agribusiness of the State of Minas Gerais, which is the largest milk producer in Brazil (28% of production). The dairy production chain is one of the most important in the state, employing labor, generating revenues of around R $ 2.4 billion/year and guaranteeing income for a large part of the population. However, most properties have low productivity due to several factors related to the herd, such as health, genetic potential and management. Among these, those related to health stand out, with mastitis being the main one. Bovine mastitis is a complex disease, defined as an inflammation of the udder resulting from the entry and multiplication of pathogens. Costs include veterinary treatment, decreased milk quality, reduced and discarded milk production due to antibiotic residues, increased labor costs, early drying-off of cows and even animal disposal. Since a few years ago, several experiments identified QTLs (Quantitative Trait Loci) that control production and reproduction characteristics, and also resistance to mastitis. Through strategies of fine mapping, some regions have been identified at the gene level, generating great applicability in the selection of desirable characteristics that use marker-assisted selection programs. Several efforts have been made to characterize changes in the expression of genes that correlate with resistance to mastitis. Thus, this project aimed to generate information about changes in gene expression associated with mastitis. In order to better understand the immune response mechanisms involved in the resistance/susceptibility to mastitis phenotype, it was quantified the relative expression of genes IL-2, IL-6, IL-8, IL-12, IFN-V, TNF- W, TLR-2, SEMA5A and FEZL in milk cells from crossbred cows healthy and with clinical mastitis and genes IL-2, IL-4, IL-6, IL-8, IL-10, IFN- eTNF-alpha from Gyr PO (Purebred) cows. The results demonstrated the expression of the IL-2 and IFN-V genes in healthy cows and TLR-2 in crossbred cows with the disease. These results allow us to outline new approaches to search for genes of resistance and carry out the introgression of them in commercial breeds. This project has financial support from FAPEMIG (Foundation for Research of the State of Minas Gerais).