Eight patients with arteriovenous malformations (AVMs) in the basal ganglionic and deep parietooccipital regions and one patient with an AVM in the shoulder region showed resorption of the isobutyl 2-cyanoacrylate cast and recanalization of the arteries after delayed follow-up angiography. All the AVMs were large, had multiple arterial pedicles, and revealed significant obliteration of the AVM immediately after embolotherapy. Although a 50-75% obliteration was achieved immediately after embolization, follow-up angiography 6-20 months later revealed almost the original status. The residual bucrylate cast was disproportionately small compared with the recanalized malformation in seven patients, while in two patients there was no evidence of bucrylate on plain films. Degradation of bucrylate probably is due to the lysosomal activity of the endothelial cells. The results from our nine patients with some degree of resorption of isobutyl 2-cyanoacrylate and six with recanalized AVMs 6-20 months after embolization suggest that operable AVMs should be excised soon after embolotherapy and inoperable AVMs should be embolized as completely as possible.