In 1994, the NIH (National Institutes of Health) issued new guidelines aimed at strengthening the inclusion of women and minorities in research populations. These guidelines mandated several major new elements to the agency's policy: among them, they stipulated that women and minorities and their subpopulations had to be included in all human participant research, not just clinical research; that the NIH would not allow cost as an acceptable reason for excluding these groups (in other words, researchers could not say that inclusion was simply too expensive); and that the NIH would initiate programs and support for outreach efforts to recruit these groups into clinical studies.
For more information, go to the National Institutes of Health Web link on the topic.