We have evaluated the role of In-111 anti-CEA (carcinoembryonic antigen) monoclonal antibody ZCE 025 in 8 patients. Three patients had a confirmed diagnosis of gastric carcinoma. Three had a confirmed diagnosis of pancreatic carcinoma. Two patients had elevated serum levels of CEA with no known primary. Each patient received 5.5 mCi In-111 ZCE 025 infused at doses of 10-80 mg. Planar and single photon emission computed tomography (SPECT) imaging at 3 and 7 days after infusion detected 9 of 12 known tumor sites and all 5 of the previously identified sites of metastasis. In-111 ZCE 025 MoAb imaging also found 6 previously unsuspected tumor sites and changed the preoperative evaluation in 50% of the patients studied. It changed the clinical management in 2 patients and established the site of primary involvement in 2 others. There were no clinical or biochemical reactions. In-111 ZCE 025 monoclonal antibody scintigraphy is a useful adjunct in the evaluation of patients with either gastric or pancreatic carcinoma. It may have a beneficial impact on the surgical decision making in these patients.