Values of blood gas, serum chloride, and potassium were tabulated for 21 dairy cows with coliform mastitis. Severe cases showed marked clinical signs such as loss of appetite and depression of digestive tract motility, and metabolic alkalosis such as an increase in blood pH, hypochloremia and hypokalemia compared with normal and mild cases (p < 0.01). The results showed that metabolic alkalosis can be detected more easily than acidosis in cases of severe coliform mastitis.