Natalia Kraft has a pretty good reason to believe in prayers: This past year, she survived breast cancer.
Now, she is part of a study to see if, in fact, prayers are answered.
"I definitely believe, still believe, that prayer and intention matters a lot," she said.
Kraft is one of 120 breast cancer survivors being studied. All are healing from reconstructive surgery.
For eight days, strangers around the world pray, or concentrate on positive thoughts for some of the participants. But not every participant is prayed for.
The rates of healing for the different groups will be gauged by measuring collagen levels in each patient. Collagen is produced as scars heal.
"Any help I can get in healing from this disease, I'll take -- especially one that's non-invasive," Kraft said. "It's cost effective. I don't really see any downside to it."
The study is funded by the federal government's National Institutes of Health, and being led by Marilyn Schlitz, who calls the subject she is examining "distant healing."
"I've been looking at claims made by healers from different traditions throughout history that they can use their minds to influence someone at a distance," Schlitz said.
Catherine Karas, a self-proclaimed healer from New Jersey, was one of the people praying. She had only a picture and a short description of her patient.
"When you do a study, what you're looking for is the truth," Karas said. "So what I hope is that [what] the study does is show us what the truth is."
However, Dr. Richard Sloan of the Columbia University Medical Center, who studies how non-physical ailments like depression contribute to physical problems like heart disease, says the current study is flawed at its core -- that it's not possible to study prayer.
"We know that there are religious orders out there that pray for all the sick all the time," he said. "We also know that family friends, members of religious congregations and others are praying for these people all the time, and that prayer is out of the control of the researchers.
"We can't test it," he added. "It's impossible to test. We can't know."
But the study's director says it is precisely because so many people believe in it that prayer must be studied.
"It's an obligation for science to begin to look, and look critically but open mindedly, at the possibility that our minds are more powerful than we previously understood," Schlitz said.
The study's results are due in 2006.
Kraft, who has no idea if she was prayed for during the study, says prayers, thoughts and good intentions have already eased her recovery.
ABC News' Miguel Marquez reported this story for "World News Tonight."