To define whether glycosaminoglycans play a role in palatal shelf movement, we studied the morphology and elevation behaviour of chlorcyclizine-treated mouse palatal shelves. Chlorcyclizine treatment was used because this agent enhances degradation of the palatal glycosaminoglycans, hyaluronate and chondroitin sulphates, with little or no effect on their synthesis. Use of in vitro and in vivo experiments enabled us to control the complicating effects of other factors on elevation. Drug-administration resulted in a reduction in shelf size, as measured by cross-sectional surface area, in the posterior two thirds of the palatal shelf. In vivo shelf reorientation was also inhibited. When elevation behaviour was observed in vitro, pronounced regional variation was noted. The anterior third of the shelf was able to reorient, the posterior two-third was not. This region also showed distinct histological changes as compared to controls. Mesenchymal cells were rounded with prominent nuclei and nucleoli and were more densely packed than in controls. These results suggest that for at least the posterior two-thirds of the palatal shelf, the intrinsic reorientation ability may in large part be linked to the acquisition of a specific temporal and spatial distribution of hyaluronate and possibly other matrix components.