Australians Barry J. Marshall (search) and Robin Warren (search) won the 2005 Nobel Prize in physiology or medicine on Monday for showing that bacterial infection, not stress, was to blame for painful ulcers in the stomach and intestine.

The 1982 discovery transformed peptic ulcer disease from a chronic, frequently disabling condition to one that can be cured by a short regimen of antibiotics and other medicines, the Nobel Prize (search) committee.

Thanks to their work, it has now been established that the bacterium Helicobacter pylori (search) is the most common cause of peptic ulcers.

"This was very much against prevailing knowledge and dogma because it was thought that peptic ulcer disease was the result of stress and lifestyle," Staffan Normark, a member of the Nobel Assembly (search) at the Karolinska institute (search), said at a news conference.

The Australians' proposal of a microbial cause instead was "very controversial and unexpected," said Goran Hansson, who chairs the Nobel committee that awards the medicine or physiology prize. "They had to spend the first few years convincing the rest of the world."

Marshall, 54, and Warren, 68, celebrated their new honor with champagne and beer.

"Obviously, it's the best thing that can ever happen to somebody in medical research. It's just incredible," Marshall told The Associated Press by telephone from the Western Australia state capital, Perth, where the pair were celebrating with family members.

Warren said he was "very excited also a little overcome," at the honor.

"The idea of stress and things like that (causing ulcers) was just so entrenched nobody could really believe that it was bacteria," Marshall said. "It had to come from some weird place like Perth, Western Australia, because I think nobody else would have even considered it."

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

Warren, a pathologist from Perth, Australia, "observed small curved bacteria colonizing the lower part of the stomach in about 50 percent of patients from which biopsies had been taken," the Nobel Assembly said. "He made the crucial observation that signs of inflammation were always present ... close to where the bacteria were seen."

Marshall, became interested in Warren's findings and together they initiated a study of biopsies from 100 patients.

"After several attempts, Marshall succeeded in cultivating a hitherto unknown bacterial species — later denoted Helicobacter pylori — from several of these biopsies," the assembly said. "Together they found that the organism was present in almost all patients with gastric inflammation, duodenal ulcer or gastric ulcer."

Based on these results, they proposed that Helicobacter pylori was involved in causing these diseases. By culturing the bacterium, they were able to make studying it and the illnesses easier.

"It is now firmly established that Helicobacter pylori causes more than 90 percent of duodenal ulcers and up to 80 percent of gastric ulcers," the assembly said in its citation.

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

The coveted award honoring achievements in medical research opened this year's series of prize announcements. It will be followed by prizes for physics, chemistry, literature, peace and economics.

The medicine prize is awarded by the Karolinska institute in Stockholm as stated in the will of Alfred Nobel, a Swedish industrialist who founded the prestigious awards in 1895.

The winners were picked by the institute's Nobel Assembly.

The process for selecting winners is extremely secretive — nominations are kept sealed for 50 years — leaving Nobel-watchers little to go on in their speculation.

The medicine prize includes a check for $1.3 million, a diploma, gold medal and a handshake with the king of Sweden at the award ceremony in Stockholm on Dec. 10.

Warren and Marshall are not the first Australians to win a Nobel Prize.

In 1973, Patrick White, the author of "The Aunt's Story" and "The Tree of Man" was awarded the 1973 Nobel Prize in literature.

Other Australian winners include John Warcup Cornforth, who won the chemistry award in 1975, and medicine winners Sir Howard Walter Florey (1945), Sir Frank Macfarlane Burnet (1960), Sir John Carew Eccles (1963) and Peter C. Doherty (1996).

Last year's laureates, Americans Richard Axel and Linda B. Buck, won for discovering how people can recognize an estimated 10,000 odors — from spoiled meat to a lover's perfume — and remember them.