The history of using the immune system as the primary weapon against cancer, intentionally or inadvertently, stretches back for at least three centuries. The probability of inducing a durable remission, when utilizing immunotherapy, depends upon three inter-related elements. They are the availability of a quantity of recognizable cancer antigens, the degree of anergy which is suppressing immunity, and the underlying structure of the immune system. Addressing the components of immune structure and function through a systematic approach of immune reconstitution will be briefly considered.