We studied the relation between Helicobacter pylori and residual gastritis in 28 patients with gastric cancer on whom distal partial gastrectomy with Billroth I reconstruction was performed over a 13-month period. They were subjected to serologic testing along with endoscopic and histologic examinations before operation and at 3, 6, and 12 months after operation. Anti-H. pylori immunoglobulin G (IgG) and serum gastrin levels were measured by serologic tests. The presence or absence of gastritis was determined endoscopically, and gastric mucosal hexosamine levels were determined. Gastritis was measured quantitatively by histologic examination in specimens taken from the gastric mucosa using Rauws' score. After the initial histologic evaluation we divided the H. pylori-positive patients into two groups: those with a Rauws' score of 0 to 3 ("weak" gastritis group), and those with a Rauws' score of 4 to 10 ("strong" gastritis group), allowing us to compare the results of our three postoperative histologic examinations of the two groups for possible significant differences. Our endoscopic examinations showed gastric mucosal inflammatory changes in both H. pylori-positive and H. pylori-negative patients at 3, 6, and 12 months after operation, but there was no significant difference between these two groups at any point. During the histologic examinations, however, anti-H. pylori IgG assay had become negative in several patients in the "weak" gastritis group at 3 months after operation and was found to have become negative in 78% of all patients in that group 12 months after operation. In contrast, in the "strong" gastritis group H. pylori infection was still evident in the patients 12 months after operation, suggesting that "strong" histologic gastritis may have some connection to H. pylori infection, whereas "weak" histologic gastritis has no such connection. The gastric mucosal hexosamine level was higher in the "weak" gastritis group than in the "strong" gastritis group both before operation and at 6 and 12 months, indicating some relation between gastric inflammatory changes and hexosamine levels in gastric mucosa. It further suggested the possibility that H. pylori plays a role in destroying gastric mucosa by depleting mucin, thus acting as one (though not the only) cause of residual gastritis after distal partial gastrectomy. In conclusion, we found evidence that there is a relation between residual gastritis and H. pylori infection, but H. pylori is not the sole cause of residual gastritis after gastric surgery. A causal relation is difficult to detect by simple analysis of histologic findings or by endoscopic observation or clinical symptoms alone.