Kanatsu-Shinohara and colleagues continue to reveal the secrets of the rare mammalian spermatogonial stem cells.Their most recent study offers a new approach by applying principles from hematopoietic stem cell research to demonstrate that cells which form a cobblestone-like underlay beneath testicular somatic cells in culture are spermatogonial stem cells.Utilization of mouse models and cell cultures shows how the chemokine,CXCL12,fits into the signalling cascade which governs the fate of these cells and hence is essential to male fertility.