Benedict made the comments Saturday to participants of a Vatican conference on adult stem cells convened under an unusual new partnership between the Vatican's culture office and a small U.S. biotech firm, NeoStem Inc.
Church teaching holds that life begins at conception. As a result, the Vatican opposes embryonic stem cell research because embryos are destroyed in the process. It supports research using adult stem cells.
Benedict said: "The destruction of even one human life can never be justified in terms of the benefit that it might conceivably bring to another."