We have studied the morphologic aspects of the duodenal bulb in relation to Helicobacter pylori infection in a large group of patients with endoscopically assessed duodenitis to learn more about the pathogenesis of nonspecific duodenitis (bulbitis) and to clarify the specific role of H. pylori. Eight duodenal biopsy specimens in the four quadrants of the first part of the bulb and four gastric antral biopsy specimens were taken in 208 patients. Specimens were fixed in formalin, or in glutaraldehyde, then slides were stained with hematoxylin and eosin, periodic acid-Schiff, and Alcian-Giemsa, and with toluidine blue for semithin sections. Duodenal histology revealed inflammation in 155 (74.5%) and H. pylori-like bacterial bodies in 153 (73.5%) of the patients; H. pylori infection in the gastric antrum was diagnosed in 173 (83.1%) of the patients. Distinguishing histologic aspects appeared to be related to the presence of H. pylori infection. We believe that the present histologic grading of duodenitis correlates better with the natural history of H. pylori infection in the duodenal bulb, and better fits the requirements of a modern classification than the classification commonly used in duodenitis. We conclude that the term H. pylori-linked bulbitis should be adopted as the proper term to identify the particular kind of duodenitis predisposing to peptic ulcer.