Advances made in research on the biology of aging and on the repair, replacement, and regeneration of tissues and organs (regenerative medicine) have drawn attention to old and new ethical issues. The principal concern among those who anticipate intervention in the aging process is whether or not attaining the power to do so is a desirable goal. The issues for those who are concerned about using human cells or tissues for research or therapeutic purposes are as follows: (1) whether the donor is, or is not, capable of giving informed consent; (2) if not, whether it is ethical for others to make that decision; and (3) whether the taking of one or a few potential lives for the benefit of many is ethically sound. When the source of the cells or tissues is a fetus or embryo, debate centers on the ethics of using tissue...