Gonad development usually involves the migration of primordial germ cells(PGCs) to the eventual site of gamete production. In zebrafish, this migration requires a signalling system comprising stromal cell-derived factor 1 (SDF1)and the G-protein coupled receptor CXCR4. On p. 4279, Molyneaux and colleagues have investigated whether PGC migration mechanisms are conserved between zebrafish and mice; they report that mice share many of the same requirements. For example, in cultured mouse embryos, exogenous SDF1 diverted PGCs from their normal route from the gut to the genital ridge. Similarly, in Cxcr4-/- embryos, germ cells did not colonise the genital ridge normally. However, Cxcr4-/-mouse germ cells still migrated from the primitive streak to the gut, whereas in zebrafish, SDF1-CXCR4 signalling is needed for this stage of migration.