It's time for a sweat-off!
"We have to collect sweat, go in the sauna. Definitely if we're in the robes, we'll sweat even more," an excited Kim said.
Kourtney didn't seem too convinced, but we all know the gluten-free mama is willing to give anything a try when it comes to her health!
"I've never heard of a sweat test and it sounds gross, but we do some pretty crazy things to get the information we need, especially when it comes to beauty and health," Kourtney explained.
The trio sat in the sauna and used three vials to collect the sweat needed for the test, but their time sweating it out proved to be too much, especially for Jonathan.
"I'm f--king going down," Jonathan said before throwing in the towel.
After realizing that a sweat test might not be the most accurate, they agreed that a blood test would be the way to go, and far less exhausting too!
Watch Kim, Kourtney and Jonathan sweat it out in the LOL clip above.
Watch brand new episodes of Keeping Up With The Kardashians Sunday at 9e|6p, only on E!