In May 2014, Dr. Francis Collins, the director of US National Institutes of Health, and Dr. Janine Clayton, the director of the US National Institutes of Health Office of Research on Women’s Health (ORWH) published a commentary in the journal Nature announcing new policies to ensure that preclinical research funded by the NIH consider both males and females. While these policies are still developing, they have already generated great interest by the scientific community and triggered both criticism and applause. This review provides a description and interpretation of the NIH guidelines and it traces the history that led to their implementation. As expected, this NIH initiative generated some anxiety in the scientific community. The use of female animals in the investigation of basic mechanisms is perceived to increase variability in the results, and the use of both sexes has been claimed to slow the pace of scientific discoveries and to increase the cost at a time characterized by declining research support
