Hormonal effects are increasingly recognized as important influences on neuronal function and, ultimately, on animal behavior. Such 'higher' behavioral effects are well studied, particularly in relation to sexually dimorphic behaviors. Yet, somewhat surprisingly, a significant proportion of more basic neuroscience research papers fail to specify the sex of the subjects used. In this brief article Karen Berkley argues that knowledge of, and controlling for, the sex of research animals is important. In addition, if females are used, their reproductive-cycle status could provide a deliberate strategy to investigate the effects of gonadal steroid hormones on biological functions.