Ten patients underwent contrast-enhanced abdominal computed tomographic (CT) carcinoembryonic antigen (CEA) measurement and murine 111In-B72.3 monoclonal antibody radioimmunoscintigraphy for recurrent or residual colorectal carcinoma. All patients had undergone primary colorectal tumour resection at a median of 3 (range 1-18) months previously. Histological analysis of pelvic tissue biopsies confirmed that six patients had recurrent or residual colorectal cancer and that four were tumour free. Whilst scintigraphy correctly showed all six patients with recurrent or residual disease, both CT and CEA measurement were correct in only four patients. In the four patients without recurrent cancer, CT was correct in two patients whilst scintigraphy and CEA measurement were accurate in three patients. Six out of the 10 patients showed marked nonspecific colonic excretion of radiolabelled antibody which was correctly interpreted in five patients. Future prospective studies comparing CT scans, CEA estimation and B72.3 radioimmunoscintigraphy in a larger group of patients with suspected residual or recurrent colorectal adenocarcinoma may help to define the respective sensitivity and specificity of these techniques.