SEDONA, Ariz.  Midway through a two-hour sweat lodge ceremony intended to be a rebirthing experience, participants say, some people began to fall desperately ill from the heat, even as their leader, James Arthur Ray, a nationally known New Age guru, urged them to press on.

“There were people throwing up everywhere,” said Dr. Beverley Bunn, 43, an orthodontist from Texas, who said she struggled to remain conscious in the sweat lodge, a makeshift structure covered with blankets and plastic and heated with fiery rocks.

Dr. Bunn said Mr. Ray told the more than 50 people jammed into the small structure  people who had just completed a 36-hour “vision quest” in which they fasted alone in the desert  that vomiting “was good for you, that you are purging what your body doesn’t want, what it doesn’t need.” But by the end of the ordeal on Oct. 8, emergency crews had taken 21 people to hospitals. Three have since died.

Mr. Ray, who calls himself a teacher of “practical mysticism” and has gained widespread exposure through writings and an appearance on “The Oprah Winfrey Show,” has come under intense scrutiny in the New Age movement that is a cottage industry here. The Yavapai County sheriff, Steve Waugh, has opened a homicide investigation, but Mr. Ray has not been charged.