These clinical and biochemical studies were made on the basis of the blood ketone bodies in 368 clinically healthy dairy cows. The result thus obtained may be summarized as follows. 1. The values for the blood ketone bodies of the clinically healthy cows varied so widely that they were statistically divided into 2 groups, viz., "normal and sub-normal groups." 2. The mean values for the ketone bodies of the normal group were 3.11 (0.99〜11.17)mg/100ml in total ketone, and 0.79 (0.22〜4.53)mg/100ml in free acetone. 3. The mean values for the ketone bodies of the sub-normal group were 39.10 (12.30〜73.80)mg/100ml in total ketone, and 8.23 (5.20〜10.50)mg/100ml in free acetone. 4. The values for free acetone, acetoacetic acid and β-hydroxybutyric acid increased in accordance with the increase of the total ketone. 5. All of the internal and external factors exerted influence upon the rise and fall of the total ketone, especially, it may be supposed that the stress of parturition, milk yield, season and feeding-management were very important. 6. It was clarified that the sub-normal group showed not only the increase of the ketone bodies but also increase of the blood sugar level and marked decrease in number of eosinophilic leucocytes
