This study was aimed at assessing the role of CT-hypotonic gaseous duodenography in the study of the pancreatic-duodenal region. Forty-two patients with malignancies in this region were examined with CT of the upper abdomen followed by CT-hypotonic gaseous duodenography (30 pancreatic head cancers, 7 main bile duct and 5 ampullary lesions). In 20 of 28 cases of pancreatic head carcinoma, CT-hypotonic gaseous duodenography yielded more pieces of information than baseline abdominal CT and was also more useful in small pancreatic head cancers, < 4 cm diameter. In 4 of these patients, CT-hypotonic gaseous duodenography better demonstrated the pancreatic lesions which conventional CT had demonstrated poorly. In contrast, CT-hypotonic gaseous duodenography was less useful in main bile duct carcinomas, depicting focal duodenal infiltration in only 1 of 7 cases. In all ampullary tumor patients (5/5), CT-hypotonic gaseous duodenography demonstrated intraduodenal lesions. The authors conclude that CT-hypotonic gaseous duodenography is a useful technique to investigate small pancreatic head cancers and the method of choice to demonstrate ampullary lesions.