They said that 72 percent of the carts they tested came back positive for fecal bacteria.
Even more alarming, half of the 85 carts tested carried potentially deadly E. coli bacteria.
"That's worse than you might find in a public bathroom. I would suggest that people think twice before plopping their babies in these things," said lead researcher Charles Gerba.
The toxic mess comes primarily from people placing packages of raw meat and chicken in their carts, said Gerba.
It also comes from "poopy-diapered babies' bottoms," being dropped into the carts' baskets.
The study also found that reusable shopping bags are vulnerable to nasty germs unless frequently washed.