Primordial germ cells (PGCs) are the earliest identifiable germ cells in the embryo. It has not previously been possible to purify PGCs from mammalian embryos at early stages of development (before they arrive in the gonads), when such cells are very low in number, are moving along different tissues toward the gonadal ridges, and are not identifiable by morphological criteria alone. We report here that the use of PGC-specific TG-1 antibody in combination with immunoaffinity adhesion to plastic plates coated with anti-mouse IgM secondary antibody allows the isolation of reasonably pure yields of migratory PGCs from 9.5- to 11.5-dpc mouse embryos.