The goal of the study was to confirm the influence of nervous processes on the sodium-potassium ratio in the blood of cows. Blood sampling was performed twice, in summer and in winter. It was found that in animals with different types of HNA, the sodium-potassium ratio in the different blood fractions was slightly different, but was within the physiological limits. In particular, the index of sodium-potassium ratio in whole blood, serum and blood cells of cows, depending on the type of HNA and the seasons was respectively 1.6–2.5 r.u., 15.1–21.5 r.u. and 0.11–0.18 r.u. It should be noted that in cows of SBM and SBI type of HNA, this indicator in different fractions of blood, regardless of the season, did not differ significantly. The strength of nerve processes in summer (r = -0.53–0.58; P < 0.05–0.01) and in winter was inversely related to the sodium-potassium ratio in whole blood, serum and blood cells of cows (r = -0.77–0.871; P < 0.001). The balance of nervous processes in summer is inversely related to the content of potassium in whole blood (r=-0.64; P < 0.01), serum (r = -0.55; P < 0.05) and blood cells (r = -0.60; P <0.01). However, in winter, the balance of nerve processes is directly related only to the content of this metal in whole blood of cows (r = 0.54; P < 0.05). The strength of nerve processes in the warm season significantly limited the content of potassium in whole blood, serum and blood cells of cows – η2χ = 0.33–0.43 (P < 0.05–0.01). Whereas in cold season the index of the strength of influence on the content of this element was much higher – η2χ = 0.52–0.69 (P < 0.01–0.001). Regression analysis determined the correlation of sodium-potassium ratio in the blood of cows with the main characteristics of nervous processes. Moreover, it was found that when the strength or balance of the nerve processes is changed by one unit, the sodium-potassium ratio in the serum and blood cells in the summer changes in the opposite direction, respectively, by 1.54–1.59 r.u. (P < 0.05) and 0.02 r. u. (P < 0.05). Whereas in winter only the strength of nervous processes limited this index in serum (b = -3.1; P <0.001) and blood cells (b = -0.03; P < 0.001), thus in winter up to 59% (P < 0.001) variations of this index in blood serum and up to 76% in blood cells could be caused by the strength of nerve processes. There was not confirmed significant dependence of sodium-potassium ratio in different fractions of blood of cows on the mobility of nervous processes (b = -0.01–0.53; P > 0.05). Significant correlation was found between the type of HNA and the sodium-potassium ratio in whole blood, serum and blood cells (F = 7.8–21.0 > FU = 3.01; P < 0.001). The season of year also greatly influenced the sodium-potassium ratio in whole blood (F = 18.5 > FU = 4.26; P < 0.001), serum (F = 10.6 > FU = 4.26; P < 0.01) and cow blood cells (F = 8.35 > FU = 4.26; P < 0.01). Therefore, the studies indicated a significant influence of the main characteristics of cortical nerve processes on the content of sodium and potassium in the blood of cows.