WASHINGTON — A new process may point the way to a useful blood test to diagnose mad-cow disease and its human version.

Until now, dissecting the brains of victims has offered the only way to detect such brain-wasting diseases in humans.

These diseases are caused by agents called prions. Researchers led by neurology professor Claudio Soto at the University of Texas Medical Branch at Galveston report they have developed a method of multiplying the number of prions in a blood sample so a blood test then can detect them.

Such a test could help prevent the spread of the disease through transfusions and could detect the illness in people or animals before it can be spread to others.

The findings, to appear in the September issue of the journal Nature Medicine, were released online yesterday.

The first known prion disease was scrapie, which has infected sheep for many years. In the 1980s, Britain had an outbreak of bovine spongiform encephalopathy, better known as mad-cow disease, which spread to Europe and other areas. Two cows have been found with the illness in the United States.

The human form of the illness is called variant Creutzfeld-Jakob disease and is thought to have originated from eating infected beef. It has killed about 180 people worldwide. Symptoms can take years to develop.

In addition to improving the safety of the blood supply, a practical test could help find infected people and animals before they show symptoms.

"It is very important because we could have an idea of the magnitude of the problem. We might be sitting on a time bomb, and 20 years from now it could be too late," Soto said.

Soto's research team infected 18 hamsters with prions. Scientists used their process to amplify the prions in blood samples from the hamsters. Blood from 12 uninfected hamsters went through the same process.

Blood tests then were able to detect the prions in 16 of the 18 infected animals.