Statement of problem. Resin-modified (light-cured) glass ionomer and polyacid-modified composite resin (compomer) restorations are popular choices for the restoration of root caries and cervical abrasion/erosion lesions, but clinical studies are relatively few and have been published primarily as abstracts. Purpose. In the absence of adequate clinical data, the marginal integrity of restorations of the above two types of material was compared in vitro. The microleakage of restorations of two light-cured glass ionomer restorative materials and of one compomer material was evaluated. Methods and material. Restorations of the three materials were placed in facial and lingual Class V cavity preparations in bovine incisors. All preparations were centered on the cementoenamel junction and were prepared with 45-degree enamel bevels. After thermal cycling, teeth were immersed in methylene blue dye, then sections of the restorations ( n = 16) were visually evaluated. Results. Dye penetration was observed at approximately 20% of restoration margins for all three materials, with the greatest incidence of severe leakage in the compomer restorations. Conclusion. No significant difference in microleakage among the three materials (ANOVA; p > 0.05) was found. (J Prosthet Dent 1998;79:261-3.)