It is now more realistic to see hormones as a collection of biologically active chemicals, each of which just happens to cause one cell to change its behaviour in response to another, rather than individually identifiable chemical signals, secreted in one place in the body and acting in another. The endocrine system and hormones have evolved to become extremely complex. ‘Changing perspectives’ shows that there are abundant examples of how contemporary understanding of hormones has been exploited to detect, prevent, treat, and cure disease. Hormones have also been used to improve human and animal performance, and, in the case of sport, sometimes abused. Future hormone research and potential future applications may challenge our ethical views.