Fire, reached in California, said he was awakened by a call from the Nobel committee.
"At first I was very excited.... Then I thought I must be dreaming or maybe it was the wrong number," he said. But then he confirmed the good news by checking the Nobel Web site.
"It makes me feel great. It makes me feel incredibly indebted at the same time," he said. "You realize how many other people have been major parts of our efforts."
Fire, who conducted his research while at the Washington-based Carnegie Institution, declined to say where he was Monday in California. "Somewhere near Stanford" was all he would say.
The announcement opened this year's series of prize announcements. It will be followed by Nobel prizes for physics, chemistry, literature, peace and economics.
Last year's medicine prize went to Australians Barry J. Marshall and Robin Warren for discovering that bacteria, not stress, causes ulcers.
The Nobel committees do not reveal who has been nominated for the awards, but that does not stop experts and Nobel-watchers from speculating on potential winners.
Alfred Nobel, the Swedish inventor of dynamite, established the prizes in his will in the categories of literature, peace, medicine, physics and chemistry. The economics prize is technically not a Nobel but a 1968 creation of Sweden's central bank.
Winners receive a check of $1.4 million, handshakes with Scandinavian royalty, and a banquet on Dec. 10 — the anniversary of Nobel's death in 1896. All prizes are handed out in Stockholm except for the peace prize, which is presented in Oslo.
