J. Robin Warren and Barry J. Marshall won the 2005 Nobel Prize in Medicine for discovering that Helicobacter pylori bacteria are the primary cause of peptic ulcers and some stomach cancers. Their finding that H. pylori infection, not stress, caused most ulcers revolutionized treatment by providing antibiotics as a cure. Though their discovery was initially controversial, they persisted in proving its significance, showing that ulcers and some stomach cancers could now be effectively treated and prevented.