The radiodensities of enamel, dentin, aluminum, and 14 modern composite resins at thicknesses of 1 to 4 mm were compared. Nine of the 14 composites were radiopaque with respect to that of aluminum. Radiolucent lesions or voids were simulated by cutting grooves 0.5, 1.0, and 2.0 mm deep in aluminum stepwedge blocks, superimposing stepwedges of the radiopaque composites over the blocks, and radiographing the combination. It was found that only five of the nine radiopaque composite materials possessed radiodensities that permitted clear radiographic detection of the smaller defects.