The Xenopus laevis embryo to the left is stained for Chordin and Hoxd-1. It illustrates the antagonism between the Spemann organiser and the non-organiser mesoderm. Over the past few years we have studied the interactions between these two types of mesoderm and their role in A-P patterning. This has resulted in a model which tries to explain how a trunk A-P pattern is generated during Xenopus gastrulation (Wacker et al. 2004a and Wacker et al. 2004b). We are investigating the role of the Spemann organiser in this model.