The Notch pathway regulates cell-fate decisions in a wide variety of cell types, often inhibiting particular differentiation programs and permitting either self-renewal or differentiation along alternate pathways. Notch receptors and Notch ligands have been found on hematopoietic stem cells (HSC) or marrow stromal cells. In the present study, through a microarray approach, we analyzed the gene expression variations from cultured murine HSC with or without a Notch ligand Delta4 at 6 hours, 12 hours and 24 hours after the induction of the Notch pathway. 13 samples against a common reference. two dye swap for each condition.