Will we still worry about Alzheimer's disease in the next century? What a question! With the population of elderly expected to double by 2025, we'll be beside ourselves with worry--unless, of course, doctors figure out how to treat Alzheimer's or, better yet, prevent it. A quarter-century from now, the number of people suffering from dementia in the U.S. alone is projected to rise from 4 million to at least 8 million. "That will bankrupt our medical system financially and emotionally," says Bill Thies, head of medical and scientific affairs at the Alzheimer's Association. "Our only alternative is to develop effective therapies."

That could happen. Over the past two decades, Alzheimer's research has exploded to such an extent that a revolution in treatment seems likely. "We now have almost an embarrassment of riches," says Dr. Kenneth Kosik, a professor of neurology at the Harvard Medical School. "Not only do we have a profound knowledge of the biology of the disease but we also have multiple targets around which drugs can be designed."

One target is a rogue protein known as beta amyloid, which forms the plaques that fill the brain's memory centers; just two weeks ago scientists identified one of the enzymes that are key to its formation. Another is an abnormal variant of the tau protein, which is thought to clutter the interiors of nerve cells with threadlike tangles. Over the coming years, as a new generation of Alzheimer's drugs enters the clinical pipeline, the arguments that rage today over which is more important, beta amyloid or tau, may be resolved. Kosik suspects that both may be critical.