Baroreceptor sensitivity was studied in twelve young normotensive subjects and forty hypertensive patients, separated into two groups according to their age, severity of hypertension and signs of severe atherosclerotic vascular disease. Under stabilized circulatory conditions, the changes of pulse rate in response to changes of blood pressure, attained by infusion of trimethaphan camphorsulfonate alone or with norepinephrine, was examined. There was gradually diminished change of pulse rate in relationship to blood pressure change as age and hypertension advanced. However, although the blood pressure threshold of stimulation was obviously higher in the middle-aged hypertensive subjects than in the normotensive ones, the slightly reduced baroreceptor sensitivity was not significantly different from that in the normotensive group. Only in the elderly hypertensive patients was significantly diminished baroreceptor sensitivity demonstrated, which was also significantly different from that in the middleaged hypertensive patients. It is speculated that the significantly diminished baroreceptor sensitivity found in the elderly hypertensive patients may be due to atherosclerotic changes in the region of the baroreceptor, although proof of that is not available at the present time.