Bone marrow consists of several kinds of cells. These cells manufacture many chemicals known as proteins. One kind of bone marrow cell (plasma cell) makes a protein called amyloid that is produced in different forms. One form is lighter in weight than others. Abnormal plasma cells may produce too much light amyloid, which results in a disease called AL amyloidosis. This protein is then deposited in different organs, causing progressive disability and death. Without treatment, patients usually die within about a year. If amyloid deposits affect the heart, death occurs more rapidly (in about 5 months). Treatment with a drug called melphalan destroys abnormal plasma cells and, when given by mouth, can lengthen survival. A promising new approach to treatment involves giving high-dose melphalan intravenously. However, this approach also kills normal bone marrow cells, which must then be replaced. This is done by collecting a special type of cell (known as stem cells) from the patient's bone marrow or blood before melphalan is administered and then giving them back to the patient (a process known as autologous stem-cell transplantation) after melphalan administration. Stem cells can regenerate normal bone marrow cells that have been lost during melphalan treatment.