C. Christopher Hook, director of ethics education for the Mayo Graduate School of Medicine, knows blood very well. As an experienced hematologist and a senior fellow at the Center for Bioethics and Human Dignity, he's done a lot of thinking about the debate over stem cells, which we glimpsed in an interview he gave to associate editor Agnieszka Tennant. Hook stressed that his comments are his own and do not necessarily represent the views of the Mayo Clinic.

Have you used adult stem cells in therapy?

I have used adult stem cells in bone marrow and peripheral stem-cell transplantation for the treatment of diseases that otherwise would be incurable. They include acute leukemias, Hodgkin's and non-Hodgkin's lymphomas, and other serious hematologic disorders.

Are adult stem cells as good a material for healing diseases as embryonic stem cells?

Because of the limited and often disappointing use of embryonic stem cells to date, one has to honestly respond that we don't know the answer to that question. However, is it really the right or most important question to ask?

The ostensible reason cited by many scientists, clinicians, and politicians for vigorously pursuing embryo destruction or cloning is the promise for creating treatments that will help, or in the best case, heal, millions of people suffering from a whole host of diseases. If that is the real goal, and you can achieve those same therapeutic benefits without having to destroy or clone embryonic human beings, then even if embryonic stem cells might prove easier to use—still a highly debatable hypothesis—it doesn't matter. You can achieve this goal without commodifying human beings in the process.

What do we know about the effectiveness of adult stem-cell therapies?

The advances ...