If you are between ages 18 and 60 and in good health, you can become a bone marrow or blood stem cell donor by joining the Be the Match registry operated by the National Marrow Donor Program. Upon registering, you will be sent a kit to collect a swab of cheek cells. If you are identified as a patient's potential match, you will be asked to undergo further testing. Hematopoietic (blood-forming) cells used in transplantations come from three sources: the blood cells of an adult donor, the bone marrow of an adult donor and the umbilical cord blood of a newborn. Adult blood stem cell donation involves inserting a needle in one arm; the donor's blood is then passed through a machine that removes the stem cells and is returned through a needle in the other arm. Most donors experience few side effects. Bone marrow donation requires surgery under general anesthesia, during which doctors withdraw liquid marrow from the hip. Umbilical cord blood is collected immediately after a child's birth and is then frozen. The registry, the biggest in the world, facilitates about 4,300 transplants a year. About 60 percent of these procedures use adult blood stem cells, 20 percent use bone marrow, and 20 percent use umbilical cord blood. Most pediatric transplants use bone marrow as the source because a study indicates that it results in better outcomes in children, according to Catherine Claeys, a spokeswoman for the donor program. According to the program, 70 percent of patients do not have a suitable donor in their family, and the chance of finding an unrelated match in the general public is about 1 in 20,000. The odds are far worse for some races and ethnic groups. The cost of adding a new member to the registry is about $100. A fee is not required to join, but donations are encouraged. You can learn more about the registry at www.bethematch.org. 