The IL-6 concentration in the serum of healthy cows ranged from 74.1–199.62 pg/mL and was not significantly different from the serum IL-6 of the entire group of mastitis cows (106.3 pg/mL vs. 78.09 pg/mL), regardless of whether the inflammation proceeded in a clinical or subclinical form (44.37 pg/mL vs. 78.09 pg/mL; 128.29 pg/mL vs. 78.09 pg/mL, respectively). This evidence concerns the gene IL6 and mastitis.