In recent years, claims have been made by segments of the research community and by women's health advocacy groups that clinical research practices and policies have not benefitted women's health to the same extent as men's health. Central to these claims has been an assertion that women have been inadequately represented as subjects of clinical studies and that as a result neither health conditions unique to women — e.g., menopause — nor women's manifestations of health problems affecting both sexes — e.g., heart disease — have been investigated sufficiently.The scientific community, including federal agencies that sponsor and regulate clinical studies, is increasingly responsive to these claims and is taking steps to raise the level of women's participation in clinical studies. Controversy and concern have surrounded these actions, however. Two of the claims that have been made are: (1) that women are more difficult to study than men because of their cyclical hormonal changes; and (2) that conducting gender-specific subgroup analyses would increase the size of study populations, raise the cost of studies, and thereby reduce the number of studies that could be performed with the limited resources available. In addition, controversy over the inclusion of women of childbearing potential and pregnant women has been particularly salient. Concerns have been expressed about avoiding potential harm to existing or potential fetuses and about the possible legal and financial ramifications of such harm. A further concern involves the perceived difficulties in enrolling women in studies and retaining them for the duration of the studies.Against this backdrop, the Office of Research on Women's Health at the National Institutes of Health (NIH) asked the Institute of Medicine (IOM) in October 1992 to establish the Committee on the Ethical and Legal Issues Relating to the Inclusion of Women in Clinical Studies. The Committee's charge was to: (1) consider the ethical and legal implications of including women, particularly pregnant women and women of childbearing potential, in clinical studies; (2) examine known instances of litigation regarding injuries to research subjects and describe existing legal liabilities and protections; and (3) provide practical advice on these issues for consideration by NIH, institutional review boards (IRBs), and clinical investigators.The 16 Committee members came from diverse backgrounds: bioethics, law, epidemiology and biostatistics, public health policy, obstetrics and gynecology, clinical research, pharmaceutical development, social and behavioral sciences, and clinical evaluative sciences. Chaired by two of the authors of this article, Ruth Faden and Daniel Federman, and coordinated by the third, IOM Study Director Anna Mastroianni, the Committee met five times over a fourteen-month period, convened a one-and-one-half day invitational workshop, and commissioned several background papers. The Committee's deliberations were complicated by the announcement of new federal policies late in its term. Specifically, the Food and Drug Administration (FDA) issued guidelines (FDA 1993) to replace its 1977 guidelines, which prohibited the inclusion of women of childbearing potential in early phases of most clinical drug trials. In addition, Congress passed the NIH Revitalization Act of 1993 (P.L. 103-43), which contains provisions mandating the inclusion of women and racial and ethnic minorities in NIH-sponsored clinical research. In February 1994, the IOM Committee publicly issued its final report and recommendations, Women and Health Research: Ethical and Legal Issues of Including Women in Clinical Studies, publishing the workshop presentations and commissioned papers in a separate volume.