British researcher John Gurdon and Shinya Yamanaka of Japan have won this year's Nobel Prize in medicine.
The prize committee at Stockholm's Karolinska Institute said that the two won the award "for the discovery that mature cells can be reprogrammed to become pluripotent".
The discovery has "revolutionised our understanding of how cells and organisms develop".
The medicine award was the first Nobel to be announced this year.
The physics award will be announced Tuesday, chemistry on Wednesday, literature on Thursday and the Peace Prize on Friday. The economics prize will be announced on October 15.
Handing out prizes worth 8 million Swedish kronor sounds straightforward enough, but barely a year goes by without some hiccup.
In 1987, the Royal Swedish Academy of Sciences woke Donald Cram in California to award him the chemistry prize. Cram, a carpet cleaner by trade, hung up.
Such problems are inevitable, says Karl Grandin, director of the Centre for History of Science at the Royal Swedish Academy of Sciences.
"You can't sit in hospitals all around the world to keep track of people."
Of course the real fuss begins once the names have been made public. In the eyes of critics, some winners do not deserve the highest honour - as in the case of Barack Obama who was given the Peace prize less than two weeks into his presidency.
Perhaps worst of all, people are overlooked. The Nobel prize can honour at most three people.
The 2008 chemistry prize went to three scientists for work on fluorescent protein but omitted Douglas Prasher, who kickstarted the field.
The winners enjoyed prestigious posts in academia; Prasher ended up driving a shuttle bus.