The depth of cure of three light-cured glass-ionomer cements was examined immediately after polymerization under the curing light and 12 hours after polymerization. The duration of illumination was also varied among groups to determine its effect on the depth of cure. Light-Cured Zionomer showed a greater immediate depth of cure than did either Vitrabond or XR ionomer. All three materials demonstrated greater depth of cure 12 hours after application of the light source, indicating that they possess dual-curing characteristics. Increasing the duration of illumination from 30 to 60 seconds significantly (P .05) increased the depth of cure for all three materials.