To evaluate the efficacy of two adhesive systems in reducing microleakage when applied with three different adhesive placement techniques. Sixty freshly extracted caries-free human premolars and molars were used. MO/DO Class II standardized preparations were performed with the gingival margin placed 1 mm above the CEJ. Teeth were randomly divided into 2 groups (group I: Prime& Bond NT, Dentsply/Caulk; group II: Single Bond, 3M Espe). Each group was divided into 3 subgroups: (A) application of 2 coats and one cure: IA-IIA; (B) 2 coats and 2 cures of each adhesive system: IB-IIB; and (C) one coat of each adhesive along with the manufacturers' B1 flowable resin (0.5-mm thick layer) cured together at once: IC-IIC. Each coat was cured for 20 s at 800 mW/cm2 using a quartz-tungsten halogen light (Elipar Trilight, 3M ESPE). Teeth were then restored using 2-mm increments of an A2 microhybrid composite (Esthet-X, Dentsply/Caulk). All teeth were stored in distilled water at 37°C for 24 h, thermocycled (500x, 5° to 55°C, 30 s dwell) and then placed in a 0.5% methylene blue dye solution for 24 h at 37°C. Samples were sectioned longitudinally and evaluated for microleakage at the gingival margin under a stereomicroscope at 20X magnification. Dye penetration was scored using an ordinal scoring system, where 0: no penetration; 1: enamel penetration; 2: gingival dentin penetration; 3: axial dentin penetration. Kruskal-Wallis and Mann-Whitney tests were used. A Mann-Whitney U-Test revealed no statistically significant difference between subgroups. Although not statistically significant, P&B NT (two coats and one cure) revealed the lowest microleakage scores. In the experimental model adopted for this study, microleakage was not affected either by the adhesive or its placement technique. Schlagwörter: adhesive system, Class II restoration, composite resin, microleakage