Twenty-seven cancer patients were accidentally exposed to lethal doses of radiation in a Spanish hospital, and most are likely to die, a health official said Friday.

Three patients already have died, the most recent one on Thursday.A judge is investigating the state-run University Hospital in Zaragoza, where radiation equipment malfunctioned over a 10-day period in December.

"We fear the worst for some of the patients," said Fernando Gomez, a spokesman for Insalud, the state health system. "We are seeking information worldwide to find someone who has experience dealing with this kind of situation."

Similar accidents involving the equipment, called a linear electron accelerator, occurred in Marietta, Ga., in 1985, in Tyler, Texas, in 1986, and at the Royal Devon and Exeter Hospital in England in 1988, but no deaths were reported.

The equipment, developed in the 1940s, destroys cancer cells by exposing them to electron impulses injected at half the speed of light. The previous three accidents were blamed on a computer software error, a malfunctioning accelerator and a mathematical error made by a doctor.

It was unclear whether human error was responsible for the Zaragoza accident. The hospital's equipment, made by General Electric, had several backup safety systems that made it less likely to malfunction, a hospital official said.

Phyllis Piano, a spokeswoman for General Electric Medical Systems in Milwaukee, said the company was working with authorities in Spain to determine the accident's cause.