Shares of Healtheon soared more than 20 percent today as the company confirmed a long-anticipated merger with privately held WebMD and vowed to use an infusion of new investments to build the biggest site devoted to healthcare on the Web.

Healtheon shares climbed 20.3750 to close at 100.6250 a share after both companies unveiled details of the deal, a stock swap with an estimated worth of $9.84 billion, as well as a $250 million investment from Microsoft. Other investors including Intel, Excite, and software wholesaler Softbank will invest another $110 million.

"This market is about speed and scale," he said. "It doesn't matter to us if a partner or a doctor pays for it...It's getting to market first and getting the physician enrolled."

Once the company has seeded the physician community, Healtheon WebMD will move to make money on a per transaction basis as doctors offices use the portal to access medical records and information, claims submissions, referrals, and lab orders-as well as buy drugs, medical equipment, and other health-care products.

"A lot of people are betting a lot of money on software to straighten out the inefficiencies of the Health care industry and that plays into Microsoft's strengths," David Restrepo, an analyst at Jupiter Communications, a market-research firm based in New York, told Bloomberg.

The merger is not expected to impact Healtheon's acquisition of Mede America, a handler of electronic health-care transactions. The company agreed to buy Mede in April in a transaction valued at about $460 million.

Combined, after the Mede acquisition, the company is worth nearly $20 billion, analysts noted.