Vascular fragility in senile people is considered to have a close connection with hypertension, arteriosclerosis and cerebral apoplexy. It is therefore necessary to check the fragility for preventive purposes. Healthy aged subjects having normal blood pressure, hypertensive aged subjects and patients having cerebrovascular disturbances were included in this study. Their capillary resistance (fragility) was measured as one index of the vascular fragility. The results were compared with other factors related to hypertension and arteriosclerosis such as blood pressure, capillary permeability, blood viscosity, platelet adhesiveness, serum lipids, with the following results.1) The capillary fragility of the aged subjects was higher in cases of higher systolic pressure.2) Fluid movement across the capillary walls was less in the group of capillary fragility, but there was not a definite tendency as regards the protein loss.3) The platelet adhesiveness in the group of capillary fragility (+++) was significantly higher than that of the negative groups (-).4) No relation was established between vascular fragility and hyperlipidemia.5) The hypertensive aged subjects and patients of cerebrovascular diseases were found to have a higher capillary fragility and there was less fluid movement across the capillary walls than in the healthy aged subjects.