Hormones shape each and every one of us, affecting almost every aspect of our lives - our height, our weight, our appetites, how we grow and reproduce, and even how we behave and feel.
This documentary tells the wonderful and often weird story of how hormones were discovered.
Presenter John Wass, one the country's leading experts on hormones, relates some amazing stories - how as recently as the 19th century boys were castrated to keep their pure soprano voice, how juices were extracted from testicles in the hope they would rejuvenate old men and how true medical heroes like Frederick Banting discovered a way to make insulin, thus saving the lives of countless diabetes sufferers.
And hormones remain at the cutting edge of medicine as we try and deal with modern scourges like obesity.