Microleakage was prevented when the margins of composite resin restorations were covered with a glaze. The microleakage occurred after the glaze was abraded and removed in vivo and in vitro. 2. The glaze margins gradually separated from the enamel as well as resin surfaces and fractured, creating steps which were apt to cause exogenous staining. 3. Although the glaze coated the restoration, thus producing a smooth surface, the roughness of the composite resin was exposed when the glaze was lost in the oral environment.