We studied three patients with internal carotid artery occlusion at the siphon who had recanaiization during 1 month of close observation. Angiography and duplex carotid sonography (DCS) were repeated serially in each patient. Blood flow patterns detected by DCS were classified into three patterns by specific angiographic changes. The distal occiusive flow pattern on DCS corresponds to internal carotid artery occlusion at the siphon angiographically, the median flow pattern on DCS corresponds to partial recanaiization, and a normal flow pattern on DCS indicates almost complete recanaiization. Since DCS can be easily repeated, the exact time of recanaiization can be determined noninvasively. In all three patients, hemorrhagic infarction observed on computed tomograms occurred at the time of recanaiization detected by DCS. DCS demonstrates that recanaiization is one of the mechanisms of hemorrhagic infarction. (Stroke 1989;20:680-686)

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