Recent progress in understanding vertebrate left/right (LR) patterning has raised important questions concerning the role of Nodal in this process.Nodal expression on the left side of the lateral plate during development acts as a left-side determinant that induces left-side-specific morphogenesis. To investigate how Nodal expression is initiated here,Yamamoto and colleagues generated conditional mouse mutants in whichFoxh1 expression — Foxh1 mediates Nodal signalling — was inactivated in the lateral plate mesoderm (LPM). Their results onp. 1795 show that Nodal signalling induces the initiation and expansion of asymmetric Nodalexpression in LPM, as well the expression of Lefty1 at the midline. These findings also shed light on how asymmetric signals are transferred between embryonic tissues during LR patterning: Nodal activity probably travels from the node to the left LPM and from here to the midline.