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past 4 years were retrospectively reviewed. Occlusion was performed under normotensive condi-tions with distal perfusion of heparinized saline for 20 minutes, or until a deficit was perceived. If 20 minutes of normotension was tolerated, hypotension was induced to two thirds of mean arterial pressure for 20 minutes, or until a deficit was perceived. RESULTS: Of 47 patients, 4 (9%) had deficits at normotension. Of the remaining 43 patients, 9 (21%) had deficits at hypotension. One patient with a positive hypotensive test occlusion underwent carotid artery sacrifice after extracra-nial-intracranial bypass without sequelae. In one of the 19 patients who clinically tolerated test occlusion with hypotension and had carotid sacrifice (surgical ligation of the intracranial carotid artery), a mild embolic stroke developed, probably from the giant carotid wall aneurysm. This patient fully recovered; MR imaging showed mild changes consistent with emboli distal to the aneurysm. Symptomatic complications were noted in 2 (4%) patients, and asymptomatic arterial dissections were noted in 3 (6%) patients. CONCLUSION: Balloon test occlusion with hypotensive challenge is safe, economical, and greatly increases the sensitivity of balloon test occlusion. The predictive value of a negative test is high. However, to determine the test’s specificity compared with quantitative imaging, controlled trials will be necessary