The transcription factor encoded by the stem cell leukemia SCL/tal-1 gene is essential for the embryonic development of haematopoietic stem cells (HSC). In an Advanced Online Publication in Nature Mikkola et al. describe analysis of mice with a conditional deletion of the SCL/tal-1 gene, generated to assess the factor's role in adult haematopoiesis (Nature 19 January 2003, doi;10.1038/nature01345). Mice containing a loxP-flanked SCL/tal-1 allele were bred with the mxCre strain in which Cre protein expression can be induced by polyI-polyC. Deletion of the SCL/tal-1 gene in adult mice did not affect the differentiation or the maintenance of myeloid or lymphoid lineages. Bone-marrow transplantation experiments demonstrated that SCL/tal-1 gene deletion did not affect contribution to all haematopoietic organs. The authors conclude that "loss of SCL/tal-1 does not seem to impair considerably HSC properties, including engraftment, self-renewal and multipotency." These results suggest that transcription factors required for HSC genesis (such as SCL/tal-1) may differ from those required for long-term repopulation and multipotency in adults.