Objective: The purpose of this in vitro study was to determine the effect of residual cariesdisclosing dyes on a dentinal adhesive system and accompanying resin composite, using microleakage as the quantifying criterion. Method and Materials: The dye pretreatment groups (10 teeth in each group, n = 60) were as follows: Group 1, Caries Detector; group 2, Cari-d-tect; group 3, Seek; group 4, Snoop; group 5, To Dye For; and group 6, control (no dye pretreatment). Circular preparations were cut on the facial or lingual surface of each tooth. Caries-disclosing dyes were placed on the preparations; this was followed by treatment with 35% phosphoric acid etchant, application of a Single-Bond adhesive, and insertion of Z-100 hybrid resin composite. Following thermocycling, the teeth were sealed with nail varnish, placed in methylene blue dye, invested in acrylic resin, labeled, and sectioned. Leakage was examined (20$ magnification) by dye penetration at the occlusal and gingival surface positions of the specimen blocks using an ordinal ranking system. The data were analyzed using two-way analysis of variance with P .05 as the significance level. Results: Results of the study showed that, at the occlusal surface position of the restorations, significantly greater leakage was exhibited by To Dye For compared to Snoop. At the gingival surface position, significantly greater leakage was exhibited by: (1) Caries Detector, Cari-d-tect, Seek, and To Dye For compared to the controls; and (2) To Dye For compared to Snoop. When comparing the same dye pretreatment groups with respect to occlusal versus gingival surface positions, significantly greater leakage was exhibited at the gingival surface positions, except for the control group. Conclusion: Our data showed that all dye groups leaked (except Snoop at the occlusal surface position), and significantly greater leakage was exhibited at the gingival surface position of all groups except the control. Snoop revealed the least leakage of all the dyes tested. Schlagwörter: caries disclosing dye, dental adhesives, dental caries, microleakage, resin composites