The specific gravity of blood was studied with special reference to dietary habitus of the subject. The materials studied were 46 student nurses and 73 housewives. The results were as follows; 1. The specific gravity of blood was in close relation to the quantity and hemoglobin content of the red corpuscles. The protein content of the plasma was proved to be another major factor of the specific gravity. 2. In the group of disqualified subjects, below 1.052 in the specific gravity, the following findings were obtained; (1) Low level of serm iron and dietary iron intake were apparent. (2) Hypoacidity or anacidity was usually present. (3) Daily labor hours and menstrual period had a close relation to the specific gravity of blood. 3. The specific gravity of blood showed seasonable changes. 4. The most effective treatment of the disqualified subjects was the improvement of dietary habits.