The association of Helicobacter pylori with an increased risk of gastric adenocarcinoma has been documented, but its mechanisms have not been elucidated. This study explored these mechanisms by addressing the relationship between H pylori and the silver-staining nucleolar organizer regions (AgNORs) in the gastric antrum. The number of AgNORs per nucleus has been correlated with proliferative rate and ploidy. The results of gastric biopsies performed before and after treatment for H pylori showed that only patients who cleared the H pylori infection had a significant decrease in the number of AgNORs per nucleus. A positive association between AgNOR counts and the severity of polymorphonuclear infiltrate could be demonstrated in patients who did not clear H pylori infection. The authors concluded that H pylori infection alters the replication cycle of the antral mucosa, inducing hyperproliferation and possibly ploidy abnormalities. Whether these alterations are induced directly by the bacterium or by the acute inflammatory infiltrate remains undecided; the data in this study suggest a possible direct effect of the polymorphonuclear leukocytes.