There is to be no more discrimination against female mice in experiments. That’s the word from the National Institutes of Health. As increasing numbers of drugs prove to work far differently for women than for men, the NIH is demanding that female animals or tissues be involved in initial lab tests. Researchers have almost exclusively dealt with male animals in the past, even while testing drugs for women, because of concerns that hormone fluctuations in females could skew results. From now on though, scientists need to ensure a level playing field for the mice.