Heparan sulphate (HS) is a linear polysaccharide found attached to protein cores at the cell surface and in the extracellular matrix. Specific sulphation patterns in HS are important for ligand recognition. 2-0-sulphation is a crucial component of most HS binding sites for protein ligands and HS 2-9-sulphotransferase (Hs2st) nulants display defects in kidney and cerebral cortex development. Embryonic fibroblasts from these mice display a distinct HS composition, however, since the mutant mice die perinatally, the influence of altered HS structure on development has not yet been determined. In this study, mouse embryonic stem (mES) cells isolated from Hs2sl mutant embryos, which can be differentiated in culture, are utilised as a model system to study effect of changes in HS structure on development.