The National Bioethics Advisory Commission employs the distinction as introduced by Harold Varmus, then NIH director, at a hearing in January 1999. Totipotent cells have "unlimited capacity. Totipotent cells have the capacity to differentiate into the embryo and into extra-embryonic membranes and tissues. Pluripotent cells "can generate all of the cell types in a fetus and in the adult that are capable of self-renewal. Pluripotent cells are not capable of developing into an entire organism." Ethical Issues in Human Stem Cell Research (September 1999) by NBAC, 6100 Executive Boulevard, Suite 5B01, Rockville, Maryland 20892-7508; www.bioethics.gov.