Several recently marketed dentinal bonding agents modify, but do not remove, the smear layer. Some controversy exists as to whether the smear layer should be left in place or completely removed from preparations to be restored with composite resin systems. This study utilized scanning electron microscopy with energy dispersive x-ray analysis to evaluate the pathway of microleakage in a composite resin restorative material that utilizes a smear layer-mediated dentinal bonding agent. Microleakage occurred at the smear layer-dentin interface and progressed into both the smear layer and dentinal tubules, suggesting that the smear layer acts as a pathway for microleakage.