Shares of WebMD surged nearly 9 percent after activist investor Carl Icahn reported acquiring an 8 percent stake in the New York-based medical website.
Shares rose to $35.20, up $2.81, boosting the company's market capitalization to $2.07 billion.
In a required filing with the U.S. Securities and Exchange Commission, Icahn wrote he bought into WebMD because the company is undervalued from a long-term perspective.
As well, the New York investor, now 76, said he may seek to have conversations with management which could suggest he wants to shake up the company.
Earlier this month, Icahn said he has no interest in investing in BlackBerry developer Research in Motion and called off his pursuit of Clorox. He is still an investor in design software developer Mentor Graphics.
Previous Icahn technology investments have included Motorola, which split in half last year, with Icahn retaining large stakes in both Motorola Mobility and Motorola Solutions; Yahoo and Siebel Systems, which was ultimately acquired by Oracle for $5.8 billion in 2005.
WebMD shares had lost more than 30 percent of their value since Dec. 31 despite being one of the most popular health-related Web sites. It reported as many as 81 million monthly page views.