"It's harder to become a donor than it is to get into MIT," joked co-founder Mark Smith (who would know, as he got his PhD in microbiology there). Of the 1,000 or so potential donors who've expressed interest on his Web site over the past two years, only about 4 percent have passed the extensive medical questioning and stool testing.
The screening process can cost up to $5,000 -- so when someone makes it through, Smith and his co-founders hold on tight.
"We get most of our donors to come in three or four times a week, which is pretty awesome," Smith said. "You're usually helping three or four patients out with each sample, and we keep track of that and let you know."