The aims of this prospective, nonrandomized phase I/II study were to evaluate (1) the safety and (2) the detection rate of tissue culture-derived, 111In-labelled anti-CEA monoclonal antibody IVP ZCE 025 in patients with primary, metastatic and occult colorectal carcinomas. 111In-IVP ZCE 025 imaging correctly identified 31 of 37 primary colorectal carcinomas, 10 of 19 hot liver metastases, 11 of 16 distant metastases and seven of seven local tumour recurrences. Previously unsuspected rumours were detected by IVP ZCE 025 imaging in 11 of 34 patients. The scans were also true negative in four patients. The overall performance characteristics of IVP ZCE 025 at monoclonal antibody doses of 1.0–5.0 mg were comparable to those obtained with 40.0 mg ascites-produced ZCE 025. No clinical or biochemical adverse reactions were encountered in the 61 patients entered into this study.