The experiment involves an artificial blood called Polyheme.
The federal government has given the company that makes it approval to use badly bleeding accident victims as test subjects, without the subjects informed consent.
The only way out is to wear a blue bracelet provided by the company.
The company says it's the only way to test such a product.
But others, including Pastor Paul Burleson of a Denver church alliance, say it turns Americans into human guinea pigs.
"If I'm in accident and I just don't happen to have this particular wristband, that I'd be a guinea pig is unconscionable," he said.