Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.