Increasing evidence suggests that higher blood velocity, by causing turbulence and high shear rates at the endothelial surfaces of arteries, may be important in the pathogenesis of atherosclerosis. In order to measure the effects of antihypertensive agents on blood velocity, an improved method has been developed for analysis of Doppler ultrasound velocity recordings. The audio signal from a Doppler velocity meter is subjected to spectral analysis; the sonagraph thus obtained is digitized with the use of a magnetic table on-line with a calculator. Four monkeys were maintained at a hypertensive baseline for six weeks by infusion of angiotensin and isoproterenol. The effects on blood velocity of 72-hour infusions of propranolol, clonidine, hydralazine, and methyldopa were studied. In doses that reduced diastolic pressure by 13--28%, propranolol decreased mean blood velocity (mv) by 17%, clonidine decreased mv by 14%, while methyldopa increased mv 12%, and hydralazine increased mv by 52% (p less than .00001). Antihypertensive drugs appear to have different effects on blood velocity; these differences may influence choice of antihypertensive drugs for the prevention of arterial disease.