Most diseases have cellular origins. The majority can be traced to simple biochemical imbalances that can often be corrected by drugs. ‘Cellular therapy’ shows that some complex diseases, such as cancer, involve gene changes. When these gene changes escape they can have a devastating effect on cell growth or function. These ‘out of control’ cells further change their genetics and develop the ability for limitless division and can gain the ability to invade other tissues. In simple terms, treating such diseases requires that the errant cells are removed, corrected, or even better replaced. Transplantation of blood cells (blood transfusion) and organ stem cell therapy are discussed.