Computed tomography (CT) of the liver was performed in 53 patients before, during and 4 to 6 hours after intravenous administration of approximately 60 g of iodine in mctrizoate. At delayed CT, contrast medium was observed in the extrabiliary ducts in 20 patients (38%) and in the gallbladder in 28 (68%) of the 41 patients with no previous cholecystectomy. The increase in attenuation of liver parenchyma at delayed CT compared with the non-enhanced baseline CT ranged between 2 and 26 HU (mean 13.9). The material was divided into three groups with regard to liver function: normal, intermediate and pathologic. In the normal group contrast medium was observed in the gallbladder in 81 per cent and in the bile ducts in 57 per cent and the mean increase in attenuation of the liver parenchyma was 14.5 HU. In the pathologic group the same parameters were 40 per cent, 7 per cent and 10.6 HU, respectively. Contrast medium in the gallbladder and biliary ducts improved the information about anatomy. Pathology of the gallbladder and tumour growth along the hepatoduodenal ligament were better demonstrated. Delayed CT is a simple and non-invasive technique that may improve planning of liver surgery.