The radiopacity of six composite resins, three resin luting cements and ten filling materials were studied. The purpose was to obtain an indication of radiopacity value of different brands within each of these groups of materials and to show differences in radiopacities of filling materials and natural tooth structures. On radiographs, the optimal densities of standardized samples were determined by computer imaging system and radiopacity values of the materials were expressed in millimeter equivalent aluminum. Within the groups of materials studied, there was considerable variation in radiopacity. The composite resins of P-50, Z100 and Prisma AP.H displayed much higher radiopacities than aluminum. Panavia resin cement was shown to be similarly radiopaque to aluminum. Generally, the radiopacity of base and filling materials appeared to be higher than that of the enamel and dentin. If materials with substantial difference in radiopacity are used in combined applications for restorative treatment of teeth, lower radiopacity can interfere with the diagnosis and detection of gaps near the restoration.