Two Americans won the Nobel Prize (search) in medicine Monday for discovering how people can recognize an estimated 10,000 odors, from spoiled meat to a lover's perfume.

Dr. Richard Axel (search), 58, of Columbia University and Linda B. Buck (search), 57, of the Fred Hutchinson Cancer Research Center in Seattle revealed odor-sensing proteins in the nose and traced how they send their information to the brain.

The Nobel Assembly at the Karolinska Institute in Stockholm said it chose the pair for the $1.3 million prize not because of any practical payoff from the work, but simply because they enhanced understanding of "the most enigmatic of our senses."

For two scientists to single-handedly map one of the major human senses is unique in the history of science, Nobel assembly chairman Goeran Hansson said.

"It's pretty amazing to be able to sit here in the 21st century and reward discoveries that explain one of the human senses," he said.

Buck said she had not even known she was under consideration. "People have said things like, 'You should win the Nobel Prize,'" she said. "I feel very honored, of course."

Axel said sharing the prize with Buck was "a joy and a deep honor. ... I'm very surprised and very happy." He also said that the work might ultimately help scientists develop better insect repellants to keep away mosquitoes that transmit malaria, for example.

In 1991, Axel and Buck jointly reported discovering a large family of genes devoted to producing different odor-sensing proteins, called receptors, in the nose. Before that, scientists could only guess at how many different receptors were needed to distinguish smells in the environment.

Scientists now know that people have some 350 to 400 types of odor receptors, each of which can detect only a limited number of odors.

When a person sniffs perfume or fine wine, for example, a mix of different types of molecules flows over the receptors in the back of the nose. That activates an array of the receptors, but only those primed to respond to those particular molecules. The brain notes which receptors are activated, and interprets this pattern as the smell.

Since any given receptor can participate in more than one pattern, "you might have a rose and a skunk being recognized by some of the same receptors," Buck said.

Axel and Buck, who worked independently following their 1991 paper, went on to show that only one kind of receptor appears on each of the 5 million or so odor-sensing nerve cells in the nose, which was a surprise. They also showed how these nerve cells are wired into the brain.

The Nobel assembly said that it is still unclear what the medical and scientific implications of the discoveries will be, but that the work could affect areas as diverse as psychology — to explain why scents often remind us of childhood — and cooking, since scent and taste are intertwined.

"It's possible, I guess, that someone down the road could use this knowledge to cook up something really delicious," Hansson said. "But I think that's pretty far in the future."

Last year's medicine prize winners were Briton Sir Peter Mansfield and American Paul C. Lauterbur for discoveries that led to the development of MRI, now widely used by doctors to get a detailed, 3-D look into their patients' bodies.

The award for medicine opens a week of Nobel Prizes that culminates Oct. 11 with the economics prize. The peace prize, the only one bestowed in Norway, will be announced Oct. 8. The physics award will be announced Tuesday and the chemistry prize will be announced Wednesday in the Swedish capital.

A date for the Nobel Prize in literature has not yet been set by the Swedish Academy, but is likely to fall on Thursday, Nobel watchers said.

Alfred Nobel, the inventor of dynamite, endowed the awards that bear his name. The awards are presented on Dec. 10, the anniversary of Nobel's death in 1896.