Four patients with gastroduodenal ulcers in the absence of Helicobacter pylori illustrate the decreasing prevalence of this microorganism. One was a 19-year-old boy with nausea, diarrhoea and weight loss caused by multiple gastroduodenal ulcers due to the Zollinger-Ellison syndrome. Another was a 36-year-old man with abdominal discomfort caused by an ulcer due to Crohn's disease. The other two cases concerned a 29-year-old man and a 68-year-old woman with relapsing ulcer disease and active bleeding, in whom no causal factors could be determined. Recent studies suggest a decreasing prevalence of H. pylori leading to both a relative and an absolute decrease of gastroduodenal ulcers attributed to H. pylori. Future treatment strategies will have to take these altered prevalence rates into consideration.