Most stem cells are in your bone marrow. We also have some in your blood that circulate from your bone marrow. Bone marrow stem cells turn into red blood cells, white blood cells, or platelets to help your body stay healthy. If our bone marrow is attacked by a disease such as multiple myeloma, it can no longer make normal blood cells. In a stem cell transplant, healthy stem cells are placed in your body through an IV to help your bone marrow start to work right. When the stem cells come from your own blood or bone marrow, it is called an autologous transplant. Autologous stem cell transplants are done using peripheral blood stem cell transplantation (PBSCT). With PBSCT, the stem cells are taken from blood. The growth factor G-CSF may be used to stimulate the growth of new stem cells so they spill over into the blood. G-CSF is a protein that is produced naturally in the body. The blood is removed from a vein and passed through a machine that separates the stem cells. The machine then returns the remaining blood through a needle in the person's arm or through a central venous catheter. This way of collecting stem cells is called apheresis.