Continuous electroencephalographic (EEG) monitoring was done during 143 consecutive carotid endarterectomies in 130 patients to detect intolerance to cross-clamping. An intraluminal shunt was inserted when EEG changes appeared (in the first 100 procedures) or when EEG changes appeared and a long clamping time was supposed (in the last 43 cases). 121 patients had no EEG changes at clamping time and only 1 had a postoperative deficit due to embolization, which occurred before clamping and was revealed by a decrease of voltage on tracing. 15 patients showed early (within 4 min after clamping) changes and in 11 patients shunting led to the reversal of EEG anomalies in all cases but 2. The state of these 2 patients was worse after surgery, in one because of embolic problems, in the other (shunted 30 min after clamping) probably for hemodynamic reasons. 4 patients with early EEG changes, not shunted because of the short clamping time, had no neurological deficit. 7 patients, 2 of which were shunted, showed late (after 4 min) EEG changes. Only 1 nonshunted patient in this group awoke with a minor, transitory neurological complication. Moreover, EEG changes have been correlated with the preoperative clinical condition and with the presence, on angiography, of contralateral carotid lesions. Also, EEG findings have been correlated with the computed tomography data (in 71 cases) and with the values of interior carotid artery (ICA) back pressure (in 58 cases). No possibility to predict the tolerance to clamping appeared from these correlations. However, a relatively higher risk of intolerance to clamping in patients with contralateral ICA occlusion was noted.(ABSTRACT TRUNCATED AT 250 WORDS)