1. Embryonic stem cells - are harvested from the inner cell mass of the blastocyst seven to ten days after fertilization.
2. Fetal stem cells - are taken from the germline tissues that will make up the gonads of aborted fetuses.
3. Umbilical cord stem cells - Umbilical cord blood contains stem cells similar to those found in bone marrow.
4. Placenta derived stem cells - up to ten times as many stem cells can be harvested from a placenta as from cord blood.
5. Adult stem cells - Many adult tissues contain stem cells that can be isolated.