Facebook is expanding the advertising system that lets marketers show ads to people on Facebook based on their online browsing interests, in the company's latest step to refine its ad business. Last fall Facebook introduced Facebook Exchange (FBX), a way for businesses to show ads to people on Facebook based on their browsing history. Now the company is launching a small alpha test to introduce FBX-targeted ads in News Feed.

"We wanted to give advertisers and agencies the opportunity to deliver highly relevant ads in News Feed, the most engaging place on the web," Facebook said in a blog post. Previously, advertisers could run standard ads on the right hand side of Facebook on the desktop. Starting today, advertisers can run Page post link ads on the right-hand side of Facebook and in News Feed on desktop. As they do today, these ads will point back to specific landing pages to help direct-response advertisers drive conversions.

Allowing advertisers to reach people in News Feed is important because people spend more time in News Feed than any other part of Facebook.

As part of this closed alpha test, Facebook is working with a small number of demand side platforms (DSPs) including TellApart, MediaMath, and Nanigans. Over the coming weeks, the company will make these ads available to additional DSPs and advertisers.