The carcinoembryonic antigen (CEA) is a clinically useful marker since it is expressed by adenocarcinomas of diverse origin. Detection and quantitation of circulating CEA levels is used to follow the clinical course of metastatic adenocarcinoma. In this phase I study, the toxicity, pharmacokinetics, and optimal imaging dose of an In-111 labeled monoclonal anti-CEA antibody (ZCE025) was studied in patients with colorectal carcinoma or any CEA-producing tumor. Twenty-four of 26 evaluable patients (92%) demonstrated at least one site of tumor-specific antibody uptake. Sixty-seven sites of metastatic cancer were identified by conventional diagnostic studies. Twenty-nine (43%) of these sites were demonstrable by radioimmune imaging using ZCE025. Twenty-five additional sites of antibody uptake were observed but could not be associated with metastatic deposits. Lymph node and visceral metastases were visualized more frequently than bone, subcutaneous, lung, or liver metastases. Neither tumor size nor antibody dose (2.5-40 mg) appeared to influence the frequency of tumor imaging. The pharmacokinetics of the In-111 labeled antibody fitted a two-compartment model, and patients receiving less than 10 mg of antibody showed a faster clearance of the antibody than those who received greater than 10 mg.