A retrospective study was carried out to determine the diagnostic value of OncoScint CR/OV immunoscintigraphy in assessing patients with suspected recurrence of carcinoma of the colon and ovary. The scintigraphic results of 31 patients were compared with surgical and histopathological findings, conventional radiological examinations and clinical disease outcome over an average 3-year follow-up. Detected lesions were divided by location into hepatic or extrahepatic and the latter group was classified as local recurrence at the resection site, pelvic or abdominal regional lymph node involvement and distant metastatic disease. The combined sensitivity and accuracy of immunoscintigraphy in the detection of extra-hepatic disease was significantly higher than that of cross-sectional radiological imaging (87% and 83% vs 44% and 53% respectively) with equal specificity of 74%. Scintigraphy identified 14 (36%) of 39 extra-hepatic malignant lesions not diagnosed by conventional radiological techniques and influenced therapeutic planning in 8 (26%) of 31 patients studied. In the liver, conventional imaging had a significantly higher detection rate than immunoscintigraphy (sensitivity 93% vs 28%). In conclusion, these results show that OncoScint scintigraphy is a sensitive method for the detection of local recurrence and extra-hepatic metastases in colorectal and ovarian carcinoma and has an important role in the therapeutic decision-making process.