Mammalian adult haematopoietic stem/progenitor cells (HSPCs) reside in the bone marrow and give rise to differentiated blood cells through asymmetric cell division. However, it has been challenging to study how HSPCs interact with other cells in the niche and whether such interactions regulate HSPC division or differentiation. Now, Manuel Théry, Stéphane Brunet and colleagues employ a microfabricated, fibronectin-coated microwell system, together with live-cell markers, to study the response of CD34+ HSPCs exposed to niche stromal cells. They show that HSPC interaction with endothelial cells and osteoblasts influences the polar localisation of HSPC cell division machinery towards the site of stromal cell contact. Osteoblast-HSPC interactions, in particular, direct the position of cell division perpendicular to the contact site. Furthermore, osteoblasts promote asymmetric HSPC division, with lysosomes and cell differentiation factors (such as CD34) inherited unequally between daughter cells, leading to greater heterogeneity. The authors show that osteoblast-induced asymmetric division relies on cytokine signalling through the SDF-1/CXCR4 pathway because chemical inhibition of CXCR4 decreases asymmetric lysosome inheritance. This work shows the importance of stromal cells in the niche in regulating progenitor cell behaviour and provides a new system with which to study HSPC dynamics.