Highly viscous gels containing sucralfate and a local anesthetic, e.g. lidocaine, were formulated for application to oral mucosa. An ex vivo bioadhesion test was performed to compare different formulations. The bioadhesiveness increases when the water content of the formulation decreases. In vitro hydration tests show that this phenomenon is related to the initial dehydration capacity of the formulation. In vitro hydration tests with two commercially available hydrophilic and hydrophobic preparations (Pansoral^® and Solcoseryl^®) gave the same results. Formulations without water (hydrophobic formulation) have better bioadhesive properties on wet mucosa than those containing water (hydrophilic formulations). Polycarbophil and chitosan loose most of their bioadhesive properties when used in hydrophilic formulations.