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To overcome the problem of poor mixing of gastrointestinal tract contents with a diluted iodinated contrast agent in abdominal computed tomography, pure water was adopted as an oral contrast agent. In 25 cases of clinically suspected gastric carcinoma, a subsequent pathological examination revealed six cases of early gastric cancer and 19 cases of advanced gastric cancer. We performed CT of the stomach using the following revised procedure: patients were given 600-1000 mL of water by mouth after an intramuscular dose of Buscopan to distend and immobilize the stomach. Gastric mucosal enhancement and the poorer enhanced submucosal layer were demonstrated by a bolus intravenous injection of iodine-containing contrast medium using an automatic injector synchronized with the CT machine. Based on abnormal gastric wall thickening and the abnormal mural enhancement patterns, an accuracy of 96% was attained in differentiating early gastric cancer from advanced gastric cancer, but the detection rates for extragastric invasion, gastric ulcers and lymphadenopathy were 67%, 43% and 63%, respectively. CT staging of gastric cancer was 72%, and was especially accurate for stages I and IV. Water as oral contrast agent for CT of the GI tract was readily accepted by patients and caused no side effects. Using water as an oral contrast for gastric CT is of great help in staging gastric cancer.