Immunosurgery is a method of selectively removing the external cell layer (trophoblast) of a blastocyst through a cytotoxicity procedure. The protocol for immunosurgery includes preincubation with an antiserum, rinsing it with hES derivation media to remove the antibodies, and the exposing it to complement. This technique is used to isolate the inner cell mass of the blastocyst. The trophoectoderm's cell junctions "shield" the ICM from antibody binding by effectively making the cell impermeable to macromolecules.

Immunosurgery can be used to obtain large quantities of pure inner cell masses in a relatively short period of time. The ICM obtained can then be used for stem cell research and is better to use than adult or fetal stem cells because the ICM has not been affected by external factors.