Two US scientists have been awarded the Nobel Prize for medicine for their pioneering work in genetics.
The work of Dr Andrew Fire and Dr Craig Mello could lead to new treatments for a range of illnesses, including viral infections and cancer.
They discovered a phenomenon called RNA interference, which regulates the expression of genes.
The process has the potential to help researchers shut down genes which cause harm in the body.
The breakthrough has also given scientists the ability to systematically test the functions of all human genes.
In its wake, many companies have been set up to develop research tools to make use of what has become a whole new industry.
Dr Craig Mello is based at the University of Massachusetts Medical School, and Dr Fire at Stanford University School of Medicine.
RNA interference occurs in both plants and animals.
It plays a key role in mobilising the body's defences against infection, and in keeping unstable genes under control.
The process is already being widely used in science as a method to study the function of genes.
The Nobel citation, issued by Sweden's Karolinska Institute, said: "This year's Nobel Laureates have discovered a fundamental mechanism for controlling the flow of genetic information."
Our genome operates by sending instructions for the manufacture of proteins from DNA in the nucleus of the cell to the protein synthesising machinery in the watery cytoplasm.
These instructions are conveyed by another form of genetic material called messenger RNA (mRNA).
In 1998, Dr Mello and Dr Fire published a paper in the journal Nature detailing how RNA interference can subvert this process - effectively shutting specific genes down.
Tiny snippets of RNA dupe the cell into destroying the gene's mRNA before it can produce a protein.
Scientists have speculated that the mechanism developed hundreds of millions of years ago as a way to protect organisms against invading viruses, which sometimes create double-stranded RNA when they replicate.
Professor Nick Hastie, director of the Medical Research Council's Human Genetics Unit, said the fact that the work had been recognised by the Nobel committee just eight years after it was published indicated just how important it had been.
He said: "It is very unusual for a piece of work to completely revolutionise the whole way we think about biological processes and regulation, but this has opened up a whole new field in biology."
Professor Hastie said previously RNA had been thought to have very little role in regulating genes - in fact some thought it nothing more than a by-product.
Dr Mello and Dr Fire's work had shown that in fact it plays a key role in gene regulation.
The Nobel Prize is worth $1.4m.