By means of Evans blue test, Rhodan-natrium method, and antipyrine test, the author estimated the contents of circulating blood-plasma, circulating blood, total body water, and intracellular and extracellular fluid in normal old persons and in hypertensive old persons; and obtained the following results. 1. The content of circulating blood-plasma in norma lold persons shows a decreasing tendency as compared with that in normal adults; and in women it is about the normal level. The volume of circulating blood in normal old persons shows a decreasing tendency both in male and female. The total body water and intracellular fluid contents are decreased whereas the extracellular fluid content shows an increase. 2. In hypertensive old persons as compared with normal old persons the contents of circulating blood-plasma, circulating blood, total body water, and extracellular fluid show a slight increase while the intracellular fluid is decreased, but the mean average of the two groups does not differ so significantly. 3. Among the hypertensive cases there can be recognized no marked difference with respect to the content of albumin in urine. 4. In relation to the systolic blood pressure, the contents of circulating blood and total body water are increased at the pressure of 160 to 200mmHg, while no great difference can be seen at the blood pressure over 200mmHg. 5. With respect to the diastolic pressure, the body fluid phase is slightly more associated with it than with the systolic pressure, but the differences between two stages is not so marked. 6. In relation with pulse-pressure it has been found that the content of total body water increases in proportion to the increase in pulse pressure. As for the relationship between the circulating blood-plasma and circulating blood male shows a positive relation while female the negative. 7. As for the seasonal relationship, the contents of circulating blood plasma and blood tend to increase in winter; the total body water in summer; while the values of both intra-and extracellular fluid phase show no variation by seasons. 8. With respect to age, the contents of circulating blood-plasma, circulating blood, and value of the extracellular fluid phase are increased at the age above 70 years, while the total body water increases at the age over 80 years.