Robin Warren and Barry Marshall have received this year's Nobel prize for medicine for discovery that Helicobacter pylori causes the majority of ulcers.
The high point in this story is that Marshall infected himself with pylori to convincingly demonstrate that it did, indeed, cause ulcers.
This discovery represented a major paradigm shift in approaching a condition that was thought of as a purely physiological response to stress and anxiety, best treated by watching what you eat. I recall back when I was at Berkeley reading a textbook on physiological disorders that preceded the widespread acceptance of this idea and discussed lifestyle changes oriented toward reducing stress and anxiety as the only treatments. It certainly made me wonder about all the other conditions in the book that were also attributed to anxiety. More paradigms waiting to shift, perhaps.