In fifteen cases of arteriovenous malformation (AVM), serial examinations of regional cerebral blood flow (rCBF) using single photon emission computed tomography (SPECT) and N-isopropyl-(123I)p-iodoamphetamine were performed. On SPECT images, the nidus was visualized as a focal rCBF defect in all cases preoperatively and seven of these cases had abnormal decreased perfusion areas in the tissues adjacent to the nidus. In five cases, the postoperative SPECT images on the day after surgery revealed an abnormal increased perfusion area adjacent to the nidus and in one case the increased perfusion was accompanied by a massive intracerebral haemorrhage detected by brain computed tomography (CT). In seven cases, postoperative SPECT images showed widespread abnormal decreased perfusion areas in the surrounding tissues and brain CT revealed either intracerebral haemorrhage or significant cerebral oedema. In the other three cases, no remarkable rCBF changes were found in comparison with the pre-operative study. There was a tendency for the preoperative abnormal decreased perfusion area adjacent to the nidus to correlate with the postoperative hyperperfusion and for the postoperative abnormal decreased perfusion area to reflect brain damage.