Hormone therapy might be an effective heart disease treatment, despite a major US study which suggested it caused harm, scientists say.
The researchers are investigating if hormones could protect women's hearts
The Women's Health Initiative study was stopped in 2002 amid concerns over raised heart disease and cancer risk.
But now other US experts say the WHI may have covered the wrong age group and used the wrong dose of HRT.
They hope a new study will pinpoint those women at risk of heart disease who would benefit from hormone therapy.
Women are protected against all forms of cardiovascular disease, including heart disease, stroke and high blood pressure, until the menopause.
But their risk then rises to be the same as men's'.
This has led researchers to conclude the sex hormone oestrogen, levels of which fall after the menopause, must be involved.
Animal studies have shown this is the case. But the Women's Health Initiative, a study of 16,000 women, found hormone therapy had no benefit - and may even be harmful.
It found the risk of heart attack was doubled in women taking a combined form of HRT, and the risk of blood clots was doubled.
The WHI also found a 26% higher risk of breast cancer in the women.
Right age group
But the average age of women in the WHI study was 63 - a decade later than the average menopause.
Virginia Miller, professor of surgery and physiology at the Mayo Clinic College of Medicine, who is one of the researchers in the new eight-centre KEEPS study, said that was too late, and women may already have an increased heart disease risk.
"If you start treatment 10 years later, that's 10 years where damage has been accumulating."
The KEEPS study will look at over 700 healthy women aged 42 to 58 who have recently gone through the menopause and are already taking hormone replacement medication.
It will also compare oral oestrogen treatment and patch therapy.
Dr Miller said: "It's important that we look at the right age group, use a lower dose than in the WHI study and compare the two forms of oestrogen therapy.
"We think there are a group of women who might benefit from early intervention.
KEEP will also monitor the progression of any cardiovascular disease that does develop in the women, and will carry out yearly mammograms to check if breast cancers are forming or being fuelled by the hormone therapy.
It will also look at the bone health and the women's' mental abilities, which might also be affected by hormone levels.
Professor Peter Weissberg, medical director of the British Heart Foundation, said that while evidence had shown women were protected from heart disease up to the menopause, suggesting hormones might have a protective effect, it was also known that female hormones could increase the risk of developing blood clots.
If a woman already had fatty deposits in the arteries, HRT might increase the risk of a blood clot developing, which could cause a heart attack, he warned.
Professor Weissberg added: "It is probable that many of the women participating in previous trials into HRT already had atherosclerosis before they started taking HRT, which lead to an increased risk of a heart attack.
"With heart and circulatory disease being the biggest killer in the UK, we welcome the Keeps study which aims to monitor women closely with new imaging techniques to search for early signs of fatty deposits.
"The trial may establish whether HRT can protect against heart disease if treatment is started early enough."