Researchers want to see whether younger women benefit from hormone replacement therapy, even though studies have shown that giving female hormones to women long past menopause can harm them. Scientists believe female hormones may prevent heart disease in younger women.

Two major studies looking at the benefits of hormone replacement in thousands of women in the United States were halted within the past few years because women given estrogen showed increases in heart disease, as well as cancers of the breast and colon, compared to women who did not take the hormones.

The results contradicted what doctors had noticed when they gave their patients hormones - those women seemed to have less heart disease than women not taking female hormones.

JoAnn Manson of Brigham and Women's Hospital at Harvard University in Massachusetts was a primary researcher in the two women's health studies.

"The pendulum has swung from the view that estrogen is good for all women, to the recent view that estrogen is bad for all women," she said. "It is becoming clear that these views are gross oversimplifications and we really need a more refined understanding of estrogen's complexity."

Researchers gave the contradiction some thought and noticed that women going to their doctors for hormones to treat hot flashes and other symptoms of menopause were much younger than the women in the large heart studies, who were generally in their 60's.

That gave them an idea, according to Mitchell Harmon, who heads the Kronos Foundation, which is sponsoring a $12 million five-year study involving 700 women. All of the participants will be within one and three years after menopause, but before heart disease usually sets in

"Our theory is that if one can start treating women during a window of opportunity, before they have had a chance to develop mature plaque, these lesions in the arteries, that the preventive effects of estrogen will predominate," he said.

Researchers will use sensitive imaging equipment to see whether there's a heart disease process in hormone treated women.

The study will be conducted by researchers at eight U.S. centers. Investigators will begin recruiting women in early September.