Many mouse somatic clones arrest at implantation with a pattern of developmental failure that resembles that of Oct4-deficient mouse embryos – a transcription factor-encoding gene required for inner cell mass (ICM) development. To investigate whether somatic clone embryonic development fails because of the incomplete reactivation of genes, likeOct4, that are required for the development of a pluripotent ICM,Bortvin and colleagues analysed the expression of 10 genes with anOct4-like embryonic expression pattern, and Oct4 itself, in cloned blastocysts derived from cumulus and ES cells. Their findings, onp. 1673, show that only 62% of cumulus-derived blastocysts correctly express all eleven genes tested, whereas ES cell-derived and normal embryos express them normally, indicating that the incomplete reactivation of such genes might contribute to the embryonic failure of somatic clones.