Australian researchers Barry J. Marshall and J. Robin Warren have been awarded the 2005 Nobel Prize in medicine for showing that bacterial infection, not stress, was to blame for painful ulcers in the stomach and intestine, the Nobel Assembly announced on Monday.

The Nobel statement said the two men's work in 1982 "made the remarkable and unexpected discovery" that gastritis as well as peptic ulcer disease is the result of a stomach infection caused by the bacterium Helicobacter pylori.

"Thanks to the pioneering discovery by Marshall and Warren, peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short regimen of antibiotics and acid secretion inhibitors," the jury said in a statement.

Before the discovery of the bacterium in 1982, stress and lifestyle were considered the major causes of ulcers. But it has now been firmly established that Helicobacter pylori causes more than 90 percent of duodenal ulcers and up to 80 percent of gastric ulcers, according to the jury.

The discovery has stimulated research into microbes as possible causes for other chronic inflammatory conditions, such as Crohn's disease, ulcerative colitis, rheumatoid arthritis and atherosclerosis, the jury said in its citation.

Marshall, 54, is a researcher at the University of Western Australia in Nedlands. Warren, 68, retired in 1999 from a pathology position at the Royal Perth Hospital.

The Medicine Prize opened this year's series of prize announcements. The Physics prize will be announced on Tuesday and Chemistry on Wednesday, and the Peace Prize on Friday. The Economics prize, awarded by Sweden's central bank, the Riksbank, is scheduled for Oct. 10.

The Literature prize is traditionally awarded on a Thursday, though the actual date is only announced 48 hours in advance.

The Nobel prizes, founded in 1895 by Swedish industrialist Alfred Nobel, the inventor of dynamite, were first awarded in 1901.

This year's laureates will receive a gold medal and share 10 million Swedish kronor (1.1 million euros, 1.3 million US dollars) . They will receive their prizes at a formal ceremony in Stockholm on Dec. 10.