Google AdSense for Feeds: "Google AdSense for Feeds

AdSense for feeds is a program that enables publishers to place relevant ads in the feeds they syndicate. Google technology understands the nuances of language, and places ads that are closely matched (or 'targeted') to the content next to which they appear. [...]

If [...] your feed has more than 100 active subscribers, you may qualify for participation in AdSense for feeds (BETA). If you'd like to participate, simply fill out the application below."