The aim of the study was to evaluatte in vitro the marginal seal in Class II resin composite restorations reinforced with glass-ceramic inserts. Forty Class II cavitie s, with the gingival margins located at the cementoenamel junction, were restored with Palfique Estelite light-cured resin composite and one of two different bonding agents, All Bond 2 and Tokuso Light Bond, with or without the inclusion of glass-ceramic inserts. The extent of dye penetration along the tooth-restoration interface was measured under an optical microscope. The marginal seal of composite restorations placed with All Bond 2 was significantly better than that of restorations placed with Tokuso Light Bond. There was significantly less microleakage in All Bond 2 restorations without glass-ceramic inserts than in All Bond 2 restorations containing glass-ceramic inserts. No significant difference in marginal seal was demonstrated between Tokuso Light Bond restorations with glass-ceramic inserts and those without inserts.