Stem cells are used to create healthy and functional cells in place of cells that are differentiated and severely damaged or diseased in our body and which can not be renewed naturally. The process of replacing a diseased cell called "cell therapy" with a healthy cell is similar to organ transplantation, the only difference being the transfer of the cell to an organ. Hematopoietic stem cells are the type of stem cells most commonly used today in the bone marrow, the forerunner of all blood cells. In Parkinson's disease, stem cells can be used to generate a specific type of nerve cell that secretes dopamine. Theoretically, these nerve cells will be able to regulate the patient's brain conduction and deliver treatment where it will restore function. Stem cells can work as an alternate and renewable resource for differentiated cells. In general, researchers are exploring the potential of adult, fetal, and embryonic stem cells to be a source of specific cells such as nerve cells, muscle cells, blood cells, and skin cells that are used to treat various diseases. Although it has been applied to a limited number of patients, it has also been demonstrated in the treatment of other potentially clinical diseases of stem cells (including diabetes and kidney cancer). Research is underway on new clinical applications for stem cell treatment of liver disease, coronary diseases, autoimmune and metabolic diseases, chronic inflammatory diseases (amyloidosis, etc.) and other advanced types of cancer.