This is a timeline of the events relating to the discovery that peptic ulcer disease and some cancers are caused by H. pylori. In 2005, Barry Marshall and Robin Warren were awarded the Nobel Prize in Physiology or Medicine for their discovery that peptic ulcer disease (PUD) was primarily caused by Helicobacter pylori, a bacterium with affinity for acidic environments, such as the stomach. As a result, PUD that is associated with H. pylori is currently treated with antibiotics used to eradicate the infection. For decades prior to their discovery, it was widely believed that PUD was caused by excess acid in the stomach. During this time, acid control was the primary method of treatment for PUD, to only partial success. Among other effects, it is now known that acid suppression alters the stomach milieu to make it less amenable to H. pylori infection.