SLAM cell-surface markers delineate differentiation steps in early hematopoiesis. Originating with pluripotent hematopoietic stem cells (HSCs), differentiation steps include multipotent progenitor cells (MPPs) and lineage-restricted progenitor cells (LRPs). Each is characterized by a different complement of SLAM markers: HSCs are CD150⁺CD48^-CD244^-; MPPs are CD150^-CD48^-CD244⁺; LRPs are CD150^- CD48⁺CD244⁺. It should be noted that CD48 is a ligand for CD244, thus CD150⁺ CD48^- is sufficient to distinguish HSCs from MPPs and LRPs. Illustration by Kenneth Probst.