This study was designed to quantitate variations in duplex ultrasound arterial flow velocities (cm/sec) in the common carotid artery and the superior mesenteric artery that were produced by changes in the angle of pulsed Doppler insonation. Duplex scanning was used to measure peak systolic flow velocity and mean velocity at angles from 30 degrees to 80 degrees; individual measurements were made at 10-degree increments in both the common carotid artery and the superior mesenteric artery in normal subjects. Peak systolic velocity in the common carotid artery varied from 86 cm/sec at 30 degrees to 168 m/sec at 80 degrees. Over the same transducer angle variation mean velocity ranged from 28 to 53 cm/sec. Similar changes in the superior mesenteric artery flow velocities were observed by varying the angle of insonation, where peak systolic velocity varied from 108 cm/sec (30 degrees) to 280 cm/sec (80 degrees), and mean velocity ranged from 29 cm/sec (30 degrees) to 71 cm/sec (80 degrees). Measurements taken from 70 to 80 degrees produced the most dramatic deviation from those taken at 60 degrees. In the common carotid artery the 70- and 80-degree angles produced 14% and 59% increases, respectively, in peak systolic velocity and 16% and 63% increases, respectively, in mean velocity. In the superior mesenteric artery 70-degree and 80-degree angles produced 16% and 120% increases, respectively, in peak systolic velocity and 17% and 111% increases, respectively, in mean velocity. At 80 degrees the percent increases in measured flow velocities for the superior mesenteric artery were significantly greater than those for the common carotid artery.(ABSTRACT TRUNCATED AT 250 WORDS)