The oculopneumoplethysmography (OPPG) test has been proposed as an effective method to identify significant carotid artery stenoses. To evaluate the clinical relevance of OPPG testing performed without carotid compression, the results of the preoperative OPPG studies, intraoperative pressure gradient measurements, and intraoperative "stump" pressure determinations were correlated retrospectively with the severity of the carotid lesions. Patients with positive OPPG test results had a mean pressure gradient of 44 mm Hg, whereas those patients with negative results had a mean gradient of 20 mm Hg. Of the patients with true-positive OPPG test results, 94% (29/31) had lesions causing at least 70% diameter reduction. However, overall accuracy of OPPG testing in this series was only 63% (33/52), as 81% (17/21) of the patients with false-negative OPPG test results also had tight lesions. Without carotid compression, OPPG testing was not useful in predicting intraoperative stump pressure. The OPPG test reflects a balance between the severity of the carotid stenosis and the adequacy of compensatory collateral flow. A positive OPPG test result is reliable in identifying those patients at greatest risk from their carotid arterial lesion. Although a negative OPPG test result does not exclude a tight stenosis, it does provide information with regard to its hemodynamic significance.