1. 1. In order to ascertain the relation of the pulse pressure to the hemodynamics of arterial hypertension, determinations of the cardiac output, blood volume, and pulse wave velocity, and oscillometric measurements have been made in twenty-five cases of hypertension with high, normal and low pulse pressures. In addition, measurements of arteriograms of the radial and ulnar arteries have been compared in seven control subjects and seven patients with arterial hypertension. 2. 2. The cardiac stroke volume and minute volume output bore no relationship to the pulse pressure in arterial hypertension. In spite of the high pulse pressure, the heart rate, stroke volume, minute volume output of the heart, and the blood volume were found to be essentially normal. The pulse wave velocity was high, and it bore a certain relation to the pulse pressure. The lumina of the radial and ulnar arteries were of the same width as in the control subjects. 3. 3. The results of the investigation are interpreted as indicating that the high systolic pressure of hypertension depends in part on alterations in the physical state of the aorta and arteries. As judged from the clinical behavior of the blood pressure, the nature of the change within the arterial wall is not uniform. In the group studied the change was of a different nature from that found as a result of aging processes. 4. 4. There are changes in the physical properties of both the arterial and arteriolar systems in arterial hypertension. The relative degree of involvement of the arteries and arterioles can vary considerably in various types of arterial hypertension. The exact nature of the changes in the arterial and arteriolar systems is not known. 5. 5. In arterial hypertension there is a remarkable homeostatic adaptation of the heart and of the circulation to the primary changes in arterial and arteriolar systems.