Computed tomography of the gastric wall after ingestion of 500-700 ml of pure tap water, followed by rapid intravenous injection of contrast medium, was performed on 24 patients with known gastric tumors. Computed tomography detected the wall abnormality in 22 of 24 cases (91%). Local gastric involvement was correctly predicted in 20 of these patients. Tumoral ulceration was only diagnosed in two of 13 proven ulcerated tumors. General acceptance and tolerance of tap water as a gastric contrast medium was good in all patients. No side effects occurred.