In four patients with major anomalies of the hepatic artery undergoing intra-arterial chemotherapy, aberrant lobar vessels were ligated and catheters were inserted into the contralateral artery. Catheter perfusion scans performed early after ligation with 99mTc-macroaggregated albumin (MAA) showed a defective perfusion of the lobe supplied by the occluded artery (0.43, 0.23, 0.11, and 0.28, respectively, as compared to the contralateral lobe). Further MAA scans performed after catheter infusion of 90,000,000 parts of degradable starch microspheres (DSM) showed a near normal perfusion of the ischemic lobe (0.91, 0.96, 0.87, and 0.98). On the contrary, simple MAA scans performed in the first two patients 114 and 135 days after ligation showed a still defective arterial perfusion of the ischemic lobe (0.60, and 0.24). The DSM-induced redistribution of flow towards ischemic portions of the liver suggests a possible new role of DSM in regional treatment of liver tumors in cases with either occlusion of aberrant vessels or "hypovascular" tumors.