Last year, Google introduced Matched Content for Adsense publishers; a free service that promotes relevant content from your site to your site's visitors, and can help to increase your page views and the time your readers spend on your site.
Unfortunately, the Matched content feature is not available to all publishers. To be eligible, you must have a site that meets Google's minimum requirements for traffic volume and number of unique pages.
To check if your blog has been approved to use Adsense Matched Content,
==> Sign in to Google Adsense
==> Click on the Settings icon at the top right corner of the site
==> Click on "Site Management"
You will see the list of your blog and you will notice the "ready" label next to the ones that have been approved for matched content.
Has your site been approved for the Matched Content feature?