Americans Mario R Capecchi and Oliver Smithies and Briton Martin J Evans won the 2007 Nobel Prize in Medicine on Monday.
They won the prize for discoveries that led to a powerful technology known as gene targeting in mice.
In the citation, the Nobel committee said the use of gene targeting has helped expand the knowledge of "numerous genes in embryonic development, adult physiology, ageing and disease."
The medicine prize was the first of the six prestigious awards to be announced this year.
