The aim of this in vitro study was to evaluate four methods of reducing the marginal microleakage of directly placed Class II composite resin restorations. Mesio-occlusal and disto-occlusal preparations with all margins confined to enamel were placed in extracted human molars. The teeth were restored with one of four techniques using multi-incremental placement, stored for 24 hours in 37 degrees C water, thermocycled, and placed in a dye solution. The teeth were sectioned in a mesiodistal direction through the restoration and evaluated for microleakage at the gingival margins. Restorations placed in conjunction with an enamel bonding agent demonstrated severe microleakage. Marginal microleakage was reduced by the use of an extended base of visible light-cured glass-ionomer cement, A BondAband, or a dentinal bonding agent.