One hundred eighty-four 99mTc-labeled macroaggregated albumin (99mTc-MAA) perfusion studies were carried out in 39 patients with histologically proven primary (four) and metastatic (35) hepatic neoplasms. Three different patterns of tumor perfusion were observed: (1) increased central radioactivity (33%); (2) decreased central radioactivity (33%); and (3) mixed and/or diffuse radioactivity (33%). Extrahepatic perfusion as evidenced by radioactive localization in the region of the stomach, pancreas, and small bowel was noted in 51%. Its presence was associated with a higher incidence of gastrointestinal complications (45% vs. 16%). Tumor arteriovenous shunting was demonstrated in 38%, showing localization of radiotracer activity in the lungs, and decreased as tumors decreased in size. The use of 99mTc-MAA infusion studies in intrahepatic arterial chemotherapy offers an excellent evaluation of catheter placement and tumor perfusion, in addition to helping to avoid gastrointestinal complications.