The hospital evacuated its emergency room at 8:30 Saturday night, treating patients in the parking lot while hazardous-material handlers, dressed in protective clothing, tested the air in the emergency room for dangerous gases. Ms. Ramirez's body was sealed in an airtight coffin and removed.

"We're being very cautious about the human aspect of who is going to have to deal with these remains and how to deal with these remains," the Riverside County deputy coroner, Alendra Birdsall, told The Press-Enterprise. The coroner's office scheduled an autopsy for Wednesday, The Associated Press reported.

Dr. Gorchinski, who is being treated at Loma Linda Medical Center, "is feeling much better," said Dick Shaefer, a spokesman for the hospital. Mr. Shaefer said Dr. Gorchinski at first had muscle spasms, was short of breath and dizzy. Doctors at Loma Linda treated her with Pralidoxine, an antidote for organophosphate poisoning, but it is still uncertain what poisoned her. Organophosphates are used in nerve gas and in pesticides like malathion.

The two nurses are also much improved after suffering symptoms similar to those of Dr. Gorchinski. Ms. Balderas, who was taken to Parkview Community Hospital, "mainly has a headache," a hospital official said yesterday. Ms. Kane, who is hospitalized at Corona Regional Medical Center, had no symptoms yesterday, hospital officials said.

But the mystery remains. What made these people ill?

As the investigation continues, medical experts are seeking to learn why the ambulance attendants were not affected and exactly where the fumes came from. One possibility is that the fumes came from hospital vents. Medical officials involved in the case could not be reached for comment yesterday.