A series of 38 patients with high gastric ulcer (GU) was examined twice a seven-year interval. One-third of the patients had an active ulcer at the second examination. Chronic gastritis was evaluated, and the level of Helicobacter pylori (HP) colonisation assessed semiquantitatively. The results were compared with age and sex matched non-ulcer controls. The GU series differed from the controls in having a higher degree of HP colonisation in gastric mucosa. The relative risks (RR) in predicting high GU connected with high HP colonisation were significantly elevated, both in the antrum (RR = 6.0-4.8) and in the corpus (RR 5.0-4.4), and still higher when combined HP colonisation values were used (RR 9.5-7.1). The persistence of active ulcer (GU+) was associated with a very high level of HP colonisation, with absence of corpus atrophic gastritis at the first examination and with young patients. Half of the GU+ patients had the maximum grade of combined HP colonisation in both examinations. The study indicates that the presence of HP infection as well as the level of HP colonisation are of importance in both the development and chronicity of peptic GU disease.