In a phase I/II study, 37 patients with metastatic liver disease, predominantly from colorectal cancer (n = 33) were treated between 1986 and 1994 by intrahepatic arterial embolization of radioactive yttrium 90 (Y 90) glass microspheres. The calculated total liver dose increased in stages from 5,000 cGy to 15,000 cGy. Mean follow-up was 8 months (range, 1 to 49). No major procedural, hematologic, or pulmonary complications occurred. Late gastroduodenal ulceration occurred early in the study at 6 to 8 weeks in three patients with a history of chronic alcohol abuse and was treated successfully medically. Of 30 patients with either computed tomography (CT) or sonography follow-up for 4 months or longer, 15 had tumor involvement in the liver that was diffuse, irregular, or infiltrating with mixed or poor vascularity and thus definitive imaging changes could not be appreciated on follow-up. In 15 patients with identifiable marker lesions with developed hypervascularity, post-treatment beneficial effects were noted. In seven of these patients followed by CT, decreased tumor attenuation and sharper definition of tumor-liver interface were noted. Findings on sonography in eight patients were increased tumor sonolucency centrally, consistent with liquefaction necrosis, and rim hyperechogenicity, consistent with calcification. A 25% to 40% decrease in area of marker lesions occurred in five patients and one other patient had small 1.0- to 1.5-cm lesions disappear temporarily on sonography. In conclusion, this method provides a feasible single-session technique for treatment of hepatic metastases. Complications are low and if the tumor pattern is nodular with some hypervascularity, beneficial effects are observed clinically and on imaging studies.