By LEE BOWMAN

The compounds have already produced positive results in animal tests, lead researcher Nand Baindur told an American Chemical Society meeting in Anaheim, Calif.

While no human tests have been done, "these compounds are predicted to be useful in the treatment of osteoporosis and related bone-deficit conditions, including bone fractures. As bone formation agents, they can potentially be given alone or in combination with agents which decrease bone loss," said Baindur, a senior scientist at Zymo Genetics Inc. in Seattle.

In humans and other animals, bones undergo continuous remodeling, with cells called osteoclasts consuming old, worn-out bone as other cells, called osteoblasts, create new bone.

Osteoporosis occurs when the replacement part of this process slows or stops, resulting in a loss of bone mass and increased susceptibility to fractures. The condition affects 15 million to 20 million Americans, most commonly people 45 years of age and older. The cost of treatments associated with osteoporosis in the United States has been estimated at nearly $4 billion a year.

Currently, the only treatments, including estrogen, work to slow the rate of bone loss, rather than replace what's been lost.

Although researchers know what proteins act to stimulate the bone producing cells naturally in the body, attempts to inject them into patients have not worked well, Baindur noted, both because the molecules are not particularly stable and they're difficult and expensive to make.

The new drugs would work one step further back in the process, stimulating the production of the proteins naturally in the body. The researchers screened tens of thousands of compounds to find three that appeared to stimulate bone morphogenic proteins. Two of the compounds are synthetic, one is natural.

The natural compound is part of a chemical class called statins, some of which are already used to treat heart disease. The researchers speculate that might make the drug the most likely for human trials, although they're still years away from having bone regenerating pills on the market.