OBJECTIVES: To evaluate microtensile bond strength and micro-morphology at the resin-dentin interfaces of two self-etching adhesive systems subjected to simultaneous mechanical and enzymatic stress. METHODS: Sixteen enamel/dentin discs were bonded with a two-step self-etching adhesive (AdheSE, n=8) and a one-step self-etching adhesive (Xeno III, n=8) to a 2mm thick resin composite layer. One resin-dentin bar was obtained per tooth. In half of the specimens of each group microTBS and micro-morphological evaluations (TEM) was performed without loading. The other half was mechanically loaded in a cholinesterase-containing solution. MicroTBS as well as ultra-morphological evaluations of the directly loaded areas using TEM were performed on the loaded specimens. RESULTS: The microTBS of the specimens (non-loaded/loaded) were of 39.6+/-14.7/35.4+/-22.1 and of 21.8+/-29.8/15.9+/-25.5 for AdheSE and Xeno III, respectively. Under TEM, both materials presented signs of nanoleakage. However, on loaded specimens the extent of nanoleakage was slightly reduced for AdheSE and no silver staining was observed on the adhesive interface of Xeno III. TEM evaluations of the specimens' loaded area revealed no decrease in the width of the adhesive interface for AdheSE. The contrary was observed in the interface created by Xeno III. SIGNIFICANCE: The adhesive interfaces created by the two-step self-etching adhesive (AdheSE) could better withstand both mechanical and enzymatic stresses on the long-term than the one-step self-etching system (Xeno III) tested in the present study.