A comparison of blood pressures measured by direct radial intra-arterial and indirect brachial automated oscillometric methods (Dinamap 1845), was performed in thirty hypertensive post-carotid endarterectomy patients. Five hundred fifty-eight "triplet" readings of systolic, diastolic, and mean blood pressure were compared. Mean differences of 18.92, -6.32, and -0.26 mm Hg, and correlation coefficients of 0.831, 0.724, and 0.776 were calculated for systolic, diastolic, and mean blood pressures, respectively. Mean differences were then calculated within incremental direct systolic pressure ranges of 20 mm Hg and found to become significantly larger with each increasing increment of pressure. These differences ranged from -0.8 to 12.6 and 20.0 to 53.3 mm Hg in the less than 160 and greater than 160 mm Hg groups, respectively, with direct intra-arterial systolic pressures significantly greater than indirect oscillometric systolic pressures in the latter group. The results demonstrate that in the hypertensive pressure range, a significant difference exists in systolic pressure measured by intra-arterial and automated oscillometric methods.