Money definitely doesn’t grow on trees, but it might be growing in your bowels. If you’re really healthy, you can sell your poop to sick people who need it for as much as $13,000 a year.

People who are infected with a bacteria called C. difficile need healthy fecal matter in their gut in order to survive — otherwise they need to be on constant antibiotic treatment. Some people with Crohn’s disease also benefit from fecal transplants. So a company called Open Biome has been facilitating fecal transplants to patients in need, and paying healthy poopers a hefty sum for their services.

Fecal matter is transferred either through endoscopy or swallowed capsules, and Open Biome has already shipped about 2,000 treatments to almost 200 hospitals, according to the Washington Post. They’ll pay you $40 per sample, plus an extra $50 if you come in 5 days a week (the donations have to be made on-site.) The only thing is, you have to be super-healthy: only about 4% of prospective donors make the cut.

Open Biome gives their anonymous donors names like Vladimir Pootin, Albutt Einstein, and Dumpledore, to help make the poop-handling thing go a little more smoothly, according to a New Yorker piece on the poop-donation industry. So who knows? Maybe you could be the next Rumpoostiltskin.

This article originally appeared on Time.com.