Fire, 47, and Mello, 45, are among the youngest in recent history to win the prize of 10 million Swedish crowns ($1.37 million). Their work, which was published only in 1998, also received remarkably swift recognition.

Through experiments with worms, the two showed that a double strand of ribonucleic acid, or RNA - the genetic messenger of the cell - can "silence" targeted genes in a process known as RNA interference (RNAi). RNAi has grown quickly into a hot area of research for pharmaceutical and biotechnology companies, who see it as a promising new way to tackle a range of conditions.

The discoveries may lead to methods to stop gene expression in diseases such as cancer, slowing tumor growth. "The discovery is already being used in clinical trials for viral diseases, for eye diseases, for cardiovascular metabolic diseases," Bertil Fredholm, a member of the prize-giving Nobel Assembly of Stockholm's Karolinska Institute, said.

"But even more importantly, it is being used in every drug industry as a fundamental research tool," he added, saying RNAi has "invaded" laboratories worldwide.

Fire earned his PhD in biology in 1983 at the Massachusetts Institute of Technology and is now a professor of pathology and genetics at Stanford University School of Medicine. Mello has a Harvard doctorate and is a professor of molecular medicine at the University of Massachusetts Medical School.

The Massachusetts school said a number of companies - Novartis AG, Bristol-Myers Squibb, Monsanto Co., GlaxoSmithKline and Pfizer - had licensed RNAi for their research.