The suitability of water as an oral or rectal contrast medium for abdominal CT was studied in 56 patients and compared with an iodine-containing water-soluble contrast medium (ioxital amino acid). In some cases it was impossible to differentiate gastrointestinal structures from extraluminal fluid collections (cystic tumours, ascites, abscesses) and there was poor filling of distal small bowel and colon. The routine use of water can, therefore, not be recommended. In some cases, however, water can result in improved image quality by reducing artifacts and improving the demonstration of the mucosa.