BACKGROUND Cerebrovascular reactivity (CVR) is the capacity of the cerebral microcirculation to increase cerebral blood flow on vasodilator stimulation. This is reduced in patients with carotid obstruction. The changes in arterial pressure produced whilst carrying out different tests for estimation of the CVR may affect its measurement by transcranial Doppler. OBJECTIVE To evaluate the concordance between the different methods for estimation of the CVR by transcranial Doppler in patients with carotid obstruction and to evaluate the importance of monitoring the arterial pressure during CVR tests. METHODS We evaluated 17 patients with internal carotid artery obstruction confirmed on arteriography. The CVR was determined by three different methods: apnea test. Breath-Holding Index (BHI) and intravenous acetazolamide test. RESULTS During the tests of RCV the arterial pressure was monitored. We found that there was a reduction in the average basal rate of flow and of the pulsatile index on the obstructed side, with a statistically significant association in relation to the contralateral side (p < 0.001). There was good concordance between the different tests of CVR, with reduced CVR seen on the obstructed side as compared to the contralateral side (p < 0.001) for the different tests. However, this correlation was not seen in stenosis < 70%. During the apnea test changes in blood pressure occurred, with a tendency to increase in the systolic pressure. However, there were no significant changes in blood pressure during the acetazolamide test. CONCLUSIONS There is good concordance in the CVR between the apnea, BHI and acetazolamide tests in carotid obstruction. Changes in arterial pressure occurred during the apnea and BHI tests. However, the acetazolamide test caused no change in arterial pressure.