Redoubling their efforts to unlock the power of the human genome, philanthropists Eli and Edythe L. Broad yesterday pledged an additional $100 million to the biomedical research center they helped launch a year and a half ago as a joint venture of Harvard and MIT.

The new funding to the Broad Institute, which doubles the $100 million originally announced by the billionaire couple in 2003, will be made through Harvard and will be distributed over 10 years.

When the initial donation was made to MIT last year, the gift was considered “seed” money for an eventual $300 million fund to be raised through donations from alumni and other donors. But during the press conference that followed the announcement yesterday, founding director of the institute Eric S. Lander avoided saying whether that goal had been reached.

“There’s lots going on with it....[The new donation] is a separate and wonderful thing that we had not in any way anticipated,” said Lander, who holds academic appointments with both Harvard and MIT.

Under a white tent in the parking lot of the temporary laboratory space that houses the institute, a crowd of more than 200 people, including University President Lawrence H. Summers and MIT President Susan Hockfield, was on hand to receive the news directly from the Broads yesterday.

“A big tent is a fine metaphor for what we are all about—the rain you can leave out,” Lander said.

Eli Broad said he and his wife decided to give the second gift because they were “impressed with the [institute’s] progress and wanted to see it accelerated.”

Research at the institute uses genetic data from the recently completed human genome project to better understand the underlying chemistry of disease. One project team is currently attempting to build an inhibitor for every human gene, and researchers just completed a catalog of human genetic variation called the Haplotype Map.

“I’m just a humble social scientist, so I don’t understand all of this,” said Summers during his remarks, “but I am an economist and I know that an investment that doubles 18 months later is a really great investment.”

Summers has pushed the expansion of the life sciences throughout his tenure and has made it a focus of Harvard’s expansion into Allston.

Summers also joked that members of the Institute’s executive committee agreed more often with Edythe Broad’s “standards” for the Institute than with Eli’s.

“Mrs. Broad would give the Broad Institute all of our money, that’s her standard,” Eli Broad said during the press conference after his announcement. “My standard is to understand the progress and to fund that progress.”

“You see why we have a particular affinity for Mrs. Broad,” Summers responded.

The institute, which currently receives $10 million from the Broads every year, will see that number double as of January 2006. It is scheduled to move to a new location at 7 Cambridge Center in Kendall Square in early 2006.

Eli Broad built his fortune over decades as the architect of two Fortune 500 companies.

Summers, who turned 51 yesterday, said during his remarks that the gift was “the largest birthday present I ever expected to receive.” The crowd responded with a rendition of “Happy Birthday.”

—Staff writer May Habib can be reached at habib@fas.harvard.edu.