HELENA -- Thirteen monkeys and dozens of hamsters died over the weekend at Rocky Mountain Laboratories in Hamilton after they were housed in 100-degree heat for several hours due to a heater malfunction.

All the animals died from excessive heat, although many other animals in the room with them were unharmed, said Marshall Bloom, associate director of the labs.

''This was just very, very unfortunate," he said.

All of the animals were involved in research on chronic wasting disease and other transmissible spongiform encephalopathies -- the family of brain-wasting diseases that include mad cow disease and a similar human ailment.

The monkeys had been inoculated with chronic wasting disease to see if primates can get the deer and elk disease either by eating contaminated foods or having infectious particles injected in their brains.

No microbes or any other dangerous material escaped the lab as a result of the accident, Bloom said, and no member of the public or lab employee was threatened.

The animals were housed in the lab's 10,000-square-foot animal research wing. The temperature in that part of the lab is not supposed to go above 78 degrees or fall below 72 degrees. Part of the heating system involves heating air over hot coils. If the air leaving the coils is too hot, an alarm will sound, Bloom said.

Sometime after 4 p.m. Saturday, the computer that controls the coil heat system ''locked up," Bloom said, forcing air to circulate over the coils and become very hot. The hot air was then piped into the animal wing, where parts of the area reached 100 degrees.

An alarm sounded, but it was not designed to contact the lab's 24-hour security desk, Bloom said, and by then, the technician who cares for the animals had gone home for the day.

The technician found the dead animals the next morning at 8 a.m. The wing was hot and the heat system was still malfunctioning.

The heating system has since been repaired and the alarm has been changed to alert 24-hour security workers if there is ever a change in temperature. The lab is also in the process of checking every alarm in the facility to make sure it rings to the security desk.

Lab officials have also contacted the National Institutes of Health in Bethesda, Md., which oversees the lab, as well as the lab's Animal Care and Use Committee, which includes members of the public.

Bloom said the accident would not jeopardize the lab's ability to work with animals in the future, and he said the lab has a long, accident-free history of working with animals.

''We, as scientists, have an obligation to respect those animals and use them in the most humane and thoughtful manner that we can," he said. ''We take the animal work here very, very seriously."

The last time a large number of animals died was about 12 years ago when a group of hamsters died after getting too hot, Bloom said.

The monkeys who died over the weekend have been autopsied and their brains prepared so scientists can see if they contracted disease.

All the animals have since been incinerated in a such a way that any infectious chronic wasting particles have been inactivated, Bloom said.

Scientists were waiting for the monkeys to show any signs of chronic wasting disease, said Bruce Chesebro, a lab scientist. About half the monkeys involved in the experiment died, which will set their research back by a year, he said. The experiment was designed to last up to five years.

Right now, no one knows if people who eat deer and elk infected with chronic wasting can become sick, as people who eat beef contaminated with mad cow disease can become sick with a similar brain-wasting ailment.

Over the next several weeks, scientists will be examining the brains of the monkeys for signs of brain wasting disease. If they find any, that information would shed new light on humans and chronic wasting disease.

''We are suspicious that they won't be positive (for chronic wasting) because it's too early," Chesebro said.

The National Institutes of Health is looking at building a new Biosafety Level 4 (BL-4) research lab at Rocky Mountain Labs that would handle deadly diseases for which there are no cure, like the ebola virus.

Critics of the lab said Thursday the dead monkeys prove their point: ''You can put safeguards in place, but accidents happen," said Alexandria Gorman, director of science and research at Women's Voices for the Earth in Missoula.