Objective: This study was undertaken to verify the hypothesis that dentin surfaces are demineralized during placement of four kinds of chemcially setting cements (zinc phosphate cement, luting lgass-ionomer cement, restorative glass-ionomer cement, and zinc polycarboxylate cement). Method and materials: Sixty cemented dentin disks were observed under scanning electron microscopy and with confocal laser scanning micrscopy after use of an argon-ion etching technique. To determine the surface effects of the cements, 30 dentin surfaces were treated with 1 of 6 freshly mixed cements (5 per group) for 60 seconds. The disks were subjected to rinsing with a water spray and ultrasonic wasing prior to scanning electron microscopic observation. Results: Observation of cemented dnetin specimens revealed that the dentin was not completely demineralized at the interface formed by the cement and dentin and that the extent and depth of demineralization along the interface tended to be nonuniform. Zinc phosphate cement caused the greatest demineralization of dentin, followed by luting glass-ionomer cement. The extent of demineralization with restorative glass-ionomer cement or zinc polycarboxylate cement was less discernible. Confocal laser scanning microscopy generally confirmed scanning electron microscopic observations and revealed that most of the specimens showed close adaptation of the cements to the dentin surfaces. Conclusion: Acid-containing cements have slef-etching properties that are effective, to various degrees, in removing the smear layer and promoting close adaptation to dentin surfaces.