Thirty immunoscintigraphic examinations were performed in 28 patients previously treated for primary colorectal (n = 12) or ovarian (n = 16) carcinomas. Occult disease was suspected from increasing serum tumor markers while conventional imaging of the extrahepatic abdomen was negative or doubtful. Head-thorax and abdomen-pelvis anterior planar images and abdomen-pelvis SPECT images were obtained 4-5 days after injection of 1 mg MAb B72.3-GYK-DTPA labelled with 111-185 MBq of 1 1 1 In-chloride. IS was positive in 26 patients. Correlative studies were achieved comparing IS results to histology for 18 abnormal extrahepatic intra-abdominal sites detected and to clinical follow up and focused conventional morphological explorations for the others. IS performances, calculated for the 28 patients, exhibited a high sensitivity (95.4%), accuracy (78.5%) and positive predictive value (87.5%) with a poor specificity (16%). IS was particularly useful for the diagnosis of carcinosis (9 TP, 1 FN) and locoregional recurrences (14 TP, 3 FP) and detected occult disease 2 to 10 months before conventional explorations in 21 patients, giving rationale for a beneficial modification of their treatment for 13 patients. No immediate clinical adverse effect was noticed.