Attention, all women: science wants you. Men have long been the subjects of clinical trials (one reason: they don't get pregnant), but the findings don't always translate to the other sex. Already, doctors know that women's bodies differ from men's (heart disease, for example--the No. 1 killer for both men and women--typically manifests about 10 years later in women). "There are big gaps in our knowledge," says Harvard's Dr. Francine Welty. Want to participate? Learn more (including critical questions you should ask before taking part) at the Society for Women's Health Research (womancando.org) and the National Institutes of Health (clinicaltrials.gov).