Cloned embryos can be produced reasonably efficiently by transferring nuclei from undifferentiated embryonic stem cells into oocytes but nuclear transfer from somatic cells is inefficient, partly because the epigenetic modifications that characterize differentiated cells must be reprogrammed. Thus, it has been proposed that adult stem cells, with their relatively undifferentiated genomes, are efficient nuclear donors. On p. 1985, Atsuo Ogura and colleagues reveal that this is not necessarily the case. They show that offspring are generated less frequently by nuclear transfer from mouse haematopoietic stem cells (HSCs) than from other somatic cells (e.g. fibroblasts). Developmental arrest occurs between the 2-cell and 4-cell stage in embryos containing HSC nuclei, and these embryos fail to activate several embryonic genes, including the chromatin-modifying enzyme histone deacetylase 1. The authors suggest that the low expression level of this enzyme is responsible for the limited developmental potency of the embryos, and conclude that the efficiency of cloning by nuclear transfer and cell differentiation status are not always reciprocally related.