TWO people have died and 19 others are being treated in hospital after becoming ill in a sauna-like "sweat dome".
The lodge at the Sedona resort which is meant to provide spiritual cleansing is now the centre of a police investigation.
In all, 21 of the 64 people crowded inside the sweat lodge on Thursday evening for the two-hour session received medical care.
Many emerged from the large, windowless dome, feeling light-headed and weak.
A man and a woman are reported to have died.
A middle-aged man and woman were reportedly unconscious and a third person was not breathing.
Dwight D'Evelyn, of the Yavapai County Sheriff's Office, said: "We are looking at pre-existing medical conditions.
"Some have indicated they may have been fasting, so there's a lot that may have played into this."
Police said participants had paid up to $9,000 (£5,600) to experience the dome, which was warmed by heated rocks brought inside.
It is based at the Angel Valley Retreat Centre near Sedona, in northern Arizona.
The retreat draws many from the New Age spiritual movement.
