During the period 1994-95, 22 patients were examined with CT during arterial portography for evaluation of hepatic tumours. The majority, 20 patients, had metastases from colon cancer. All patients were candidates for liver resection. In the series of patients described here, this process detected additional lesions in four more of the patients than found with any other imaging techniques. This supports that CT during arterial portography is the most sensitive method for detecting small malignant hepatic tumours, and for localizing them in relation to liver segments and major vascular structures. Optimal results are obtained in the absence of diffuse parenchymal disease and portal hypertension. Non-tumourous perfusion defects limit the accuracy of this technique, but such defects have characteristic locations and appearance. In difficult cases the technique should be correlated with ultrasonography and MR.