The launch, which Facebook is calling a "small alpha test," brings Facebook Exchange-targeted (FBX) ads, which are special ad units served to members based on their online browsing behavior, to the desktop version of News Feed for the first time.
"We wanted to give advertisers and agencies the opportunity to deliver highly relevant ads in News Feed, the most engaging place on the Web," the company wrote in a blog post. "We also believe that ads delivered through FBX will create more relevant ads for people."
The addition of the ad unit will not change the total number of ads people see in their News Feeds, the company said.
In October, the company exclaimed that it was making $4 million a day from the in-stream, Sponsored Story placements by the end of the third quarter 2012.
But since the social network reported fourth-quarter earnings in late January, and stayed mum on revenue from News Feed ads, investors have been increasingly skeptical of the company's ability to grow revenue as it spends more. The stock has slid backward, down about $6 per share, or 20 percent, since it closed at $31.24 on Wednesday, January 30.
Investors haven't exactly rallied around today's reveal, but Facebook's shares are trading up by a few cents Tuesday. Perhaps there's something to this Plan B.