The effectiveness of a dentin-bonding agent (DBA) and a glass-ionomer cement liner (GIC) in reducing the marginal microleakage at the cervical margin of Class II posterior composite restorations was examined. The effect of load cycling on microleakage of this type of restoration was evaluated. The Class II cavities were prepared in extracted human pre-molar teeth, with the cervical margins finished approximately 1 mm below the CFJ. Combinations of DBA, GIC, and control (no liner) were used as mediators between resin and dentin. All restorations were placed incrementally with a 40-second cure per increment and finished with high-speed diamond burs. Half the samples of each treatment group received cyclical axial loading and half did not. All samples were thermocycled at 5° and 55°C for 500 cycles of one min each, stained (four hr) in 50% AgNO3, and sectioned following stain development. Microleakage was scored linearly along the dentin-restoration interface. All restorations exhibited microleakage which was unaffected by load cycling. Both the DBA and the GIC significantly reduced microleakage independently. When GIC was present, the additional presence of the DBA did not provide a statistically significant additional reduction of microleakage.