The article discusses the persistent sex bias in neuroscience and biomedical research, highlighting the underrepresentation of females in studies, particularly in animal models. Despite the NIH's mandate for female inclusion in human clinical trials, similar initiatives for animal research are lacking. A review of 10 biological fields in 2009 revealed a male bias in 8 disciplines, with male-only studies outnumbering female-only studies by 5.5 to 1. This bias has increased in non-human studies over the past 50 years while declining in human studies. Many studies fail to analyze results by sex, leading to a limited understanding of female biology. The majority of articles use rats and mice, excluding other useful models. The belief that female mammals are more variable is unfounded, and the article recommends indicating single-sex studies in titles and favoring proposals that study both sexes and analyze data by sex. Historical analysis shows that in the early 20th century, few studies specified subject sex, but this increased over time. By 1969, male-only studies became more common, and by 2009, over 85% of articles in neuroscience, pharmacology, immunology, and physiology focused on rodents. Species diversity in behavior, zoology, and reproduction was higher. In human studies, male bias was less prevalent, with more studies analyzing both sexes. However, in non-human studies, male bias remained high, with few studies analyzing results by sex. The article emphasizes the importance of studying both sexes to understand sex differences in diseases, as many conditions are more prevalent or severe in women. It highlights the need for sex-specific analysis in research, as ignoring it can lead to incorrect conclusions. The article also discusses the impact of estrous cycles on research and the importance of considering hormonal variations in study design. It recommends that journals require specification of subject sex and that funding agencies prioritize studies that include both sexes. The article concludes that studying multiple species is essential for valid comparisons and that the neglect of females in research has hindered progress in understanding diseases affecting women. The article calls for a shift in research practices to ensure that both sexes are studied and that sex differences are properly analyzed.The article discusses the persistent sex bias in neuroscience and biomedical research, highlighting the underrepresentation of females in studies, particularly in animal models. Despite the NIH's mandate for female inclusion in human clinical trials, similar initiatives for animal research are lacking. A review of 10 biological fields in 2009 revealed a male bias in 8 disciplines, with male-only studies outnumbering female-only studies by 5.5 to 1. This bias has increased in non-human studies over the past 50 years while declining in human studies. Many studies fail to analyze results by sex, leading to a limited understanding of female biology. The majority of articles use rats and mice, excluding other useful models. The belief that female mammals are more variable is unfounded, and the article recommends indicating single-sex studies in titles and favoring proposals that study both sexes and analyze data by sex. Historical analysis shows that in the early 20th century, few studies specified subject sex, but this increased over time. By 1969, male-only studies became more common, and by 2009, over 85% of articles in neuroscience, pharmacology, immunology, and physiology focused on rodents. Species diversity in behavior, zoology, and reproduction was higher. In human studies, male bias was less prevalent, with more studies analyzing both sexes. However, in non-human studies, male bias remained high, with few studies analyzing results by sex. The article emphasizes the importance of studying both sexes to understand sex differences in diseases, as many conditions are more prevalent or severe in women. It highlights the need for sex-specific analysis in research, as ignoring it can lead to incorrect conclusions. The article also discusses the impact of estrous cycles on research and the importance of considering hormonal variations in study design. It recommends that journals require specification of subject sex and that funding agencies prioritize studies that include both sexes. The article concludes that studying multiple species is essential for valid comparisons and that the neglect of females in research has hindered progress in understanding diseases affecting women. The article calls for a shift in research practices to ensure that both sexes are studied and that sex differences are properly analyzed.