Other than swelling at a cut, and maybe some pus or a slight fever, we would be forgiven for not being aware of the existence of the human immune system. It is however a highly complex system, and when it is overwhelmed, things can get a lot more serious. In this informative and engaging program the three levels of immune defence are explored in isolation and as part of a disparate yet interconnected system. High quality animations are used to illustrate the nature of specific and nonspecific defence mechanisms deployed by the human immune system. The role of human intervention in the defence against disease is also explored.